@tippfehlr
You place any number of subvolumes in to main subvolume (subvolid=5), the same place where @ and @snapshots are placesd, and then add all you subvolumes into fstab using subvol mount option. So the root subvolume does not contain any nested subvolumes, caches, logs and whatever you would not want to keep in your snapshots.

You may try to install #Garuda or #EndeavourOS and #OpenSUSE in VM with btrfs root and see how partitioning is done there.

Also I prefer snapper's / OpenSUSE way to mount root subvolume from mutable snapshot but in Arch this requires some hacks to get it done.