Btrfs is amazing for a steam library. The single best feature is the compression. Games tend to have lot of unoptimized assets which compress really well. Because decompression is typically faster than your disk, it can potentially make games load faster too.

I put a second dedicated nvme drive in my PC just for steam. It's only 512GB but it holds a surprisingly large library.

I use Fedora which defaults to BTRFS and never once had an issue with any game because of it. Your file system shouldn't matter for gaming at all so long as you stay on Linux native ones and avoid NTFS Windows drives.

BTRFS is worth it. It's a bit faster than ext4. And with BTRFS assistant or snapper, you can configure automatic snapshots of your OS partition. And grub-btrfs will allow to integrate them to the boot menu. Once you are booted via snapshot, there is a way to replace / file system with that snapshot permanently, or you can boot to another one.

And remember, snapshots in BTRFS is just a formal thing, use them only if you specifically need their features, like read only sub volumes. If you just need to backup some directory, for example with steam games, no need to do the actual snapshot. You can easily backup large amount of data with just cp -dr dir dir_backup no matter how large is it, it will be done immidetelly and without taking additional space.