You seem to look at it quite pessimistically imho, but I’ll try and counter ;-)

developers won’t support a third platform

We’re not talking about a vastly different ecosystem. Probably Android-derived (which is open-source), very likely Linux derived. So compatibility is not going to be a huge issue, hence developing not hard. Developers will usually follow where user demand goes, not the other way around.

nor will customers move to a platform that doesn’t have the big apps that they need

Most of the big apps today have a smaller equivalent, check AlternativeTo.net.

Doubling your market share is easy when your market share is so low.

Generally true, but we’re talking a growth of millions of users a year. Millions of people is no small number. 5% of the US’ traffic are from Linux desktops, according to StatCounter (here’s an article with many links).

Nope, not in the tens of millions

You’re correct wrt. gaming, as 2.89% of 157 million active monthly users is about 4.55 million, which is not a small number either.  If you look at Linux desktop users in the US however, we’re talking over 5% of 347 million, which is 17.35 million users in the US alone, which is also not a small number. It’s more than the population of Greece and Bulgaria combined.

Purely because of the steam deck (wrt. Steam Linux users growth)

Do you have numbers? I can’t find any official numbers of active users on the Steam Deck, but there are estimations of 3+ million devices sold. I feel like I keep seeing posts of people who move over to Bazzite and similar distros these days for the sake of playing games, but nevertheless, both of these factors weigh in, and are steadily increasing the adaptation of Linux systems.

without [kernel level anti-cheat] it will never take off because the overwhelmingly most played games all have kernel level anti-cheat.

This is denying the antecedent. The amount of games, and money in games, without KLAC is plenty substantial to make a difference in the approach of both developers and DRMs, further increasing ease of adaptation by users. Do not undermine nor underestimate the potential of marginalities.

The Windows phone entered the market while the market was stable, and users had little reason to move away from what they were used to and comfortable with. These days users are getting more uncomfortable, hence why Linux is on the rise. Same with the push for more liberal software (FOSS). I believe if a company can do it right, and offer a stable and comfortable alternative, they can manage to be much more successful than the Windows phone was 10 - 15 years ago.

Disclaimer: I haven’t checked the statistics, but I remain optimistic, and continue making choices that align with my principles.

Availability in the US might be a bit of a challenge, as the Google/Apple duopoly has solidified greatly over the years there. Europe has the entire BoycottUS movement these days, so there are a lot of attempts at developing something independent there. But as with most new solutions, they have the added difficulty of being compared to these bigger companies who’ve already had many years to develop and perfect their solutions.
The choice boils down to how much you value your principles over comforts, and whether downgrading to physical cards is worth it. Personally I’ve recently done just that.

In regards to Android clones becoming worse, I saw GrapheneOS say on Mastodon that it won’t affect them in any significant way. Hopefully this is the case for most, and will remain the case.

/e/OS works with most, according to this list.

The founder of /e/OS has a blog where he talks about alternative payment solutions, and he mentions Curve being one.

I just recently ordered the Fairphone with /e/OS, and will be looking into this myself soon enough…

Not a lot currently, but what’s needed is for the snowball to start rolling. This means the early adopters will have to make the more difficult decision of choosing “lesser” options wrt. comfort and convenience, compatibility, and bang for your buck. All decisions matter, and it will have long-term effects en masse.

While I can agree with the sentiment (we’re living in an unforgiving world), I also believe it’s a big matter of perspective. There is good in the world, and losing sight of it will easily land you on the highway to rumination. So as helpful as these drugs are for the biological addiction, the psychological one is a different yet vital chapter of a healthy mind (which can also be assisted by drugs).