I don’t really get the logic of how stealing from them is somehow supporting them.

You’re still in the ecosystem even if you’re not paying for it, meaning if you’re trying to pass on files or knowledge, it’s all based within Adobe’s apps and their user experience. You can look into how Adobe encourages piracy on students because that means when they get to make a choice later on what professional apps they’ll use they’ll keep using Adobe, thus if someone else asks “oh how should I get into design?” They’ll hear about Adobe as well.

Besides, every alternative is absolute garbage compared to Photoshop.

Open source sadly yes, I’ve yet to find something as good. Consider looking at the Affinity suite though, I used that for years while freelancing instead of Photoshop and illustrator and i wasn’t missing Adobe. If anything it was an improvement, so much more performant and moving across apps was a lot easier.