alt Hacker NewsXFS filesystems do not have a "/lost+found" directory in their normal state.
In the very rare occasions when one has to run "xfs_repair", it will create a "/lost+found" directory, if it is required for recovered files.
After the repair and after investigating whether the recovered files contain useful data or not (and after moving the useful files elsewhere), one should normally delete the "/lost+found" directory, because it is no longer needed.
XFS as implemented in RHEL8+ (the only places i've used it in anger) tends to handle being full very badly, leading to system lockups and blocked tasks necessitating a hard reboot. Worse yet is when it's in this state the journal fills and nothing can be done with the volume.
To recover from this on a volume mounted at boot mandates going to either a live disk, or stopping boot in initramfs and running xfs_repair there, I've fruitlessly attempted to play back the journal on many separate occasions by attempting to mount the filesystem (again causing a lock up due to no space) in that state you have to drop the journal, run xfs_repair and then clean up the detritus from /lost+found (and then the location that caused the disk to fill altogether).
EXT4 has other issues certainly, but at least it reserves blocks for the root user explicitly so the system doesn't stop.