How would you have handled this opening?

That's remarkable 

Sorry, I was misremembering the game and was thinking only of the later position in the game, where you indicated "same thing is going on here."  You're right that e3 was backward earlier in the game. So what's your question -- why did Ding decide to play f4?  I'm not sure of all the considerations myself, but someone else can probably give you a decent answer.

But it seems like you've been trying to point to something else you want to hear, without quite saying what it is.

You write "The main question would be why worry about the backwards e3 pawn? f4 in Liren's game shows that f2 supporting e3 is not enough." I guess I understand what you mean by the first half of that, but not the second half (not enough for what?), or, really how the two questions fit together.  And I'm a little unclear who's e3 pawn is being worried about and who's doing the worrying (Ding?  You?  Is this limited to Ding's game?  Your second sentence makes me think taking Ding's game as a way to think about general principals).

So I'm not really sure how to answer it until you're clearer about what you're asking.  But from what I can understand of the question:  Just to state the obvious, the backwards pawn on e3 can't be supported by another pawn and is therefore more likely to be lost, especially since it's on a semi-open file with a rook and queen bearing down on it.  If your question is, "how can it be a weakness if a strong player like Ding played it?" the answer is that strong players accept weaknesses all the time when they determine they're worth incurring because of other considerations.  He evidently calculated that the weakness could be managed and that he was getting enough kingside play out of the pawn thrust to justify it.

Here's a quote from Kmoch's Pawn Power in Chess. I will also translate some of his technical terms, and give a diagram:

"A half-free Pawn on the second or third rank, whose stop-square lacks Pawn protection but is controlled by a sentry, is called a backward Pawn (or alternatively, a straggler)."

Now, to translate:

Stop square : the square that a Pawn (especially, a backward Pawn) would need to cross in order to advance.

Sentry : an enemy Pawn that guards the stop square and prevents a backward Pawn from advancing.

Half-free Pawn : a friendly Pawn that has no enemy Pawns on the same file, but has both friendly and enemy Pawns on adjacent files. In the following diagram, the White e-Pawn is half-free :

The Black b-Pawn is both half-free and backward. The stop square is b6. White's a-Pawn is the sentry.

Secret chess refers to assessing the eval from any position. Chess refers to the game and game theory.

The secret chess is looking for black and white,aka Silman,aka what is the best move authors....whereas chess is more grey at times, with moves having a pro and con at those times.

The answer in your case is 'it depends'....saying just because white has a backwards pawn means white is worse or better, is not true. To assess the situation of any opening has to be made in the context of the middle game plans. So the question is do you know what white is planning and how to deter it.

And an even more important question is are you supposed to know. If one knows how to defend stonewall but loses quickly to grob, then they are in violation of strategy. So the way to not be, is to build an education on building blocks of chess info...like every other subject. Otherwise no matter how smart you attempt to sound, everyone knows who is pretending and who is not. Expecting an answer by internet is another lame excuse for laziness.

"Expecting an answer by internet is another lame excuse for laziness."

I think that is a little harsh don't you? After all, Coronavirus has made all a bit lazy. Just look at Carlsen's hair and beard.

"I guess I understand what you mean by the first half of that, but not the second half (not enough for what?)"

If we are to avoid backward pawns, then Liren's decision to play f4 would not substantiate this. There has to be another reason for him to play f4 creating a backwards pawn on e3. Or, is there something like "a rook on the file of a backwards pawn makes it quasi-backwards"? Liren placed a rook on e1 before he played f4.

"the answer is that strong players accept weaknesses all the time when they determine they're worth incurring because of other considerations."

DING DING DING!! No pun intended, but that is what I am trying to get at!!! What are those other considerations?

"He evidently calculated that the weakness could be managed and that he was getting enough kingside play out of the pawn thrust to justify it."

We don't know how he arrived at that decision. Could be calculation, could be following some principle/principles.

I can see what you explained, but how does it relate to Ding's f4 move or the e3 backward's pawn? Or is there another point you are making?

Are you SURE you read my explanation?

How is Ding's e3 Pawn backward? Where is the enemy Pawn that controls the stop-square e5?

I don't see one.

EDIT: Look again at my comment in Post #103, immediately following your post of the Ding game. I pointed out then and there that Ding's e3-Pawn is NOT backward.

Well, he means earlier in the game.  But he wasn't very clear about that.

I was referring to e3 as a backward pawn at this position.

"Well, he means earlier in the game.  But he wasn't very clear about that."

I can only focus on one position. I focused on the position where e3 could capture d4.

It doesn't matter where the focus is. If Ding Liren had a backwards pawn in the game, he had a backwards pawn. It doesn't disappear from the game because I focused on move 27.

I'm not going to be able to give you a good answer on this because I'm not a strong enough player to really understand this game, which has a lot of tactical and positional intricacies (and I'm not particularly familiar with these sorts of pawn structures myself).  And I'm sorry to put it this way, but if I'm not, you probably aren't either.  To understand stonewall structures, you (and I) would undoubtedly do better to study more straightforward games like the Petrosian-Korchnoi game I posted or books that feature more pedagogically useful examples, like Kmoch's, which is fascinating.  Soltis also has a pawn structure book that's supposed to be pretty good.

"To understand stonewall structures, you (and I) would undoubtedly do better to study more straightforward games like the Petrosian-Korchnoi game I posted or books that feature more pedagogically useful examples, like Kmooch's, which is fascinating."

That's fine, but right now I don't have confusion with those games. I can see what is being explained.

Referring to the Ding game:

Again, if you were willing to learn from someone below 2700, Kmoch's Pawn Power in Chess answers your question.

Starting in the diagram in post #138 above, the next four moves shield the backwardness of e3 and remove most of the drawbacks of White's chosen line (while retaining the advantages).

White played f2-f4, making his e3-Pawn backward, yes... but then he immediately played N(d2)-f3 then to e5; shielding the Backward Pawn from pressure down the file and negating most of the drawbacks of the Pawn formation while still retaining the advantages (the strongpoint on e5 for the Knight),

"but then he immediately played N(d2)-f3 then to e5; shielding the Backward Pawn from pressure down the file and negating most of the drawbacks of the Pawn formation"

So, you are saying Re1 had nothing to do with it? Why was it played then?

To prevent Qxe3+, perhaps? How else does White play f4 without giving away the e-Pawn?

To me, that sounds like Re1 is there to protect the (future) backwards pawn then.

In the crudest sense of the term, yes... but the immediate capture of the backward Pawn is only one of the drawbacks to that formation. The occupation of the stop-square (especially by an enemy Knight) can be even more damaging.

The whole thread is about poor trolling. For the record, the O.P. predictably closed his account.