But Apple can't just pay-up every cross-platform software developer. Smaller developers will have to re-evaluate whether macOS remains a viable target platform for them. Which can translate to a dev-gain for Linux. The catch is that Linux is in much better position to translate an influx of developers to an influx of new users: Linux runs on what you have, while macOS requires you buy Apple hardware.

And let's not forget about macOS as a gaming platform. Linux has made a huge leap forward with Steam Proton. On macOS there's still a ton of games not supporting x86_64 (Catalina), and situation won't get better by transition to ARM.

I’m sure that's not the case. It's much more in Adobe’s interest to be ARM-ready on day 1; there are plenty of Photoshop alternatives in the Mac App Store—notice they demoed Affinity Photo running on the ARM Mac and Affinity is much better at using Apple's native APIs and technologies than Adobe every was. And it's just a one-time cost of $49.99 vs. renting Photoshop from Adobe. Users of Apple devices are continue to be a large segment of their customer base.

Adobe has already migrated all of their core applications to a new codebase that should be relatively easy to bring to ARM Macs. Photoshop and several other of their apps already runs on iPadOS, so it won't be that big a deal to move it over to Big Sur.

So nothing is changing. ARM Mac isn’t going to change the Linux desktop/laptop story.

Hence why plenty just target Android, although some of their apps could easily be targeting GNU/Linux as well (specially the ones that are mostly NDK glue + whatever framework).