Hello,
Why on one machine I have
4 /var/tmp/flatpak-cache-3VUAC1
4 /var/tmp/flatpak-cache-DDS6C1
and on my laptop:
631472 /var/tmp/flatpak-cache-BYZHD1/child-oci-toPwKS/blobs/sha256
...
one answer could be that /var/tmp is for temporary files.
*and* /tmp and /var/tmp gets cleaned periodically by systemd-tmpfiles-clean.service.
AFAIK, once per day.
more to read:
systemctl list-timers => systemd-tmpfiles-clean.service
man systemd-tmpfiles