Delete the existing file /usr/share/icons/bloom/icon-theme.cache
, install the package normally without forcing, and don't sweat it. That cache can (and should automatically) be recreated afterwards with gtk4-update-icon-cache /usr/share/icons/bloom
, but it's strictly not critical.
The previous version of the package did not include this file, lending credibility to the assumption of a packaging mistake, as does the existence of an issue for that problem already.
Just fix this nag yourself as described, and expect this to be fixed by the packager eventually.