Rapid v Blitz

As long I know, the most increment popular to 10 mins is 5 ( 10l5 ).

I don't see 10|5 in the options.  I see 5|5.

For a typical 40 move game 5 seconds per move gives 200 seconds, so that's 8 min 20 sec, so still more time pressure than 10.

You won’t see it. But I just stated that 10l5 is the most popular increment in 10 mins. You can see it in lichess.

#1
"Isn’t this just blitz basically?"
++ Yes, indeed.
B.1
A ‘blitz’ game is one where all the moves must be completed in a fixed time of 10 minutes or less for each player; or the allotted time plus 60 times any increment is 10 minutes or less.
https://handbook.fide.com/chapter/E012018 

well, if you want less time pressure, try 15|10. I did until I got fast enough the extra time just helped my opponent. just pick the highest time control you actually use.  

I’m playing 10 on chess.com.

It seems there’s two steps to improvement:

1.play better at the same time per move

2.move faster at the same move quality.

I’m more worried about 1 right now which means if I lose some games on time, then fine.  Winning or losing is as much about how the opponent plays as it is about me, and that’s out of my control.  Best to focus on how well I play and not as much on the win or loss.  So I run game review on every game.  A win because I was out-blundered isn’t as good as a well-played loss.

Yea i was just bi*ching about this a couple weeks ago, it would be nice to have atleast 10+3 so there is no flagging nonsense

As a noob, i prefer rapid