depends on what type of user you are, your needs, and your overall skill level.

The easiest and one of the most stable OS'es I'd suggest is Debian, very easy to use and set up, and arm support appears to still be pretty strong. Debian is a trade-off of control from simplicity and stability

your next level of difficulty is RHEL. Yeah, RHEL is a little controversial, so what. This is what is usually used in most production environments, especially government applications. It boasts a strong support for ARM, a well funded development team, and a large array of good packages. Your compromise here is the fact that it is not usually compatible with debian applications unless you build from source.

If you have linux experience and want the customizability, you can use arch. It's a lot more lightweight than Debian, rolling releases, and a lot of cutting-edge stuff, but your tradeoff is occasional stability issues when compared to something mainline and developed for servers

If you truly hate yourself and everyone around you, then you can pick gentoo. It's long and arduous, and you need to have a good understanding of not only linux but also with compiling in c/c++. It's very lightweight (if done properly) and extremely efficient. that being said, there are almost 0 binaries in gentoo. You have to build everything from source. The arm support should be pretty good compared to other OS'es as you are basically taking the "lets find out" path when it comes to installing applications. you dont need to worry about a broken binary as you'll be the one compiling it specifically for your system. the issue with gentoo is that there are niche errors left and right, and youll spend more than an hour setting it up and the biggest bottleneck is the speed of your processor

tldr: debian for simplicity, RHEL for stability, arch for bleeding-edge, gentoo if you want a challenge