Text file busy / btrfs returned an error: 256 / Failed to create snapshot can occur if you have a Linux swapfile mounted within the @ or @home subvolumes which prevents snapshot from succeeding. Relocate the swapfile out of @ or *@home, for example into it's own subvolume like @swap.
ID 257 gen 975 top level 5 path @
ID 258 gen 968 top level 5 path @cache
ID 259 gen 972 top level 5 path @log
ID 262 gen 25 top level 257 path var/lib/portables
ID 263 gen 26 top level 257 path var/lib/machines
ID 272 gen 880 top level 5 path timeshift-btrfs/snapshots/2021-12-08_18-54-43/@