@KestrelPi
Luck is a subjective view of probabilistic events. Not deterministic or conscious efforts, such as skill in chess. There is no objective chance or luck in chess.
Now we're getting somewhere! So what you're saying is that in order for luck to be involved the events have to be in some way... probabilistic. Can we define that a little more so we can see if that's robust?
I promise, I'm not doing this to be annoying: it's my suspicion the reason people can't agree on this is that we're all working with different ideas of what luck is. So I've proposed one, to see if it holds up. Maybe your one holds up better
Probabilistic event involves a random mechanic that is out of the players control. They typically use dice for this purpose in games. Two players making conscious decisions with superior ability and move prevailing is not an example of such, it is the opposite of random and therefore cannot provide an instance of luck.
Superficially it does seem like there is no luck in chess, as there is no random mechanic in the game itself. But - even if we discount external events over which a player has no control - I think you could argue that chess does contain luck because no human player has a perfect understanding of the moves they make.
To give a very basic example: if I move a pawn, intending to attack my opponent's knight, and inadvertently block a checkmate threat from a bishop-queen battery that I haven't seen, what is that, if not luck? It certainly isn't skill.
This seems only to illustrate a skill differential and not that luck exists, however. It's a skill differential, which genuinely causes wins and losses.
But the differential here is not necessarily between me and my opponent, but between my objective strength and the strength of the move I played. I chose a very basic example to illustrate the concept but perhaps made it too basic. Alternatively, consider a complex middlegame - perhaps a player identifies three candidate moves. A very strong player calculates all three, realises why two of them are inferior, and plays the third. Skill. A weaker player cannot calculate all the way, but perhaps gets close enough to get a feel that that third is stronger, and plays that. Still skill, although partly subconscious. But a third player, slightly weaker still, genuinely has no idea. All the moves seem equally good. He picks one. Maybe it is right, maybe it is wrong. Clearly, there is a skill differential between him and the first two players. But whether the skill difference manifests in that moment is down to luck, or chance if you prefer - did he happen to pick the strongest move, even though they all seemed equal to him?
An opponent's blunder is NOT luck. It is a lack of skill. Is this really so hard to understand?