The question is really: what is your goal? You say Open Source software development - which software are you talking about? Are there certain projects you're looking at? Are you looking at starting your own project? Are you trying to move the open source ecosystem forward generally? (Also, what is your current skillset? Are you just getting into development or are you fairly experienced already in other platforms?)

If it's the first, follow the project and see what they're doing. If it's the second: look at the requirements. Most likely though, you will be stuck with Android, because the iPhone is even worse, and Linux on phones is far from being daily driver worthy for the vast majority of people. Alternatively, as people mentioned, you could try a Cross-Platform framework, but do be aware that these have downsides, as well. If it's the third: why not try to see what you can do to improve the situation of Linux on phones? Depending on what you're already capable of, you may already have the prerequisites to move that area forward, something badly needed IMO.

I'm long behind on Android development. I stopped not long after Google promoted Kotlin as the primary language for Android development. I really liked Kotlin though. Still these days, I'd probably go with react native or flutter. I always hear about people using those and see job postings for those in regards to android. I'd be interested in using Kotlin Multiplatform and hoping that builds up momentum and becomes super successful

Yes.

kotlin is a great programming language. The ui (compose) can also be used in kotlin multi platform to make desktop apps. You'll have to learn about lifecycles etc but it'll be worth it in my opinion

If I had the time, I would try Kotlin Compose Multiplatform. That way I would hopefully be able to learn Kotlin (good language), have fun with my GrapheneOS, be able to test on iOS, and maybe be more employable without having to handle Google's stupidity.

You can publish your open source app on Google Play, and this will not change. Google is also not planning to introduce $100/year publishing fee for devs like Apple, you pay $25 one time to register. There is also no real alternative open source OS for phones.

Google decision impacts apps like Termux, who use old Android API to install additional packages. If you are not planning to create Linux emulator, I guess this won't impact you.

Unless you're willing to get raped by the sheer amount of google's surveillance, I'd say no You will be required to present your government ID, pay 25$ and other shit just to get a chance at getting approved and distributing your software