iOS isn't relevant to Valve due to the way Apple chooses to do business, so why bring that up?

It is relevant to Apple customers that care about playing games and don't need to care Valve exists at all.

In other words, it's not relevant to the discussion at all.

Apple costumers get by with Apple's risible video game offerings, which still compromises mostly of waiting lounge pasttime shovelware and glorified slot machines, by buying computers from other manufacters (Microsoft, Nintendo, Sony, Windows/Linux PCs, Steam, etc.)

Or they use their iDevices, which have plenty of games already.

Maybe of casual and gacha games. Unless iDevice users want to miss out on the highest selling [1] and highest rated [2] AAA games their only option is directing money to other companies.

[1] https://www.gamespot.com/articles/top-10-best-selling-games-...

[2] https://en.wikipedia.org/wiki/The_Game_Awards#Awards_ceremon...

Valve says "99% of our players don't use MacOS, so we're dropping support for that."

You say "MacOS users play other games, so Valve leaving doesn't matter"

Pretty much the same thing, isn't it? If anything, it seems like you're angrily confirming Valve's decision.

What about after sideloading is allowed?

The vast majority of mobile games are not really substitutes for PC games the way e.g. console games are, except in the super broad "Netflix: Our biggest competitor is video games because customers only have so much time" way.