If you create a new sandbox with Unimarc, the items in the sample data have no itemtype (which is now mandatory) Left empty it now breaks the Opac details page (see BZ 32747) so if you don't know about it you cannot test a unimarc patch on the opac. Wasn't sure which component and severity to choose, so feel free to change it
You couldn't find a component because the sample data comes from an external project, https://gitlab.com/koha-community/koha-misc4dev
https://gitlab.com/koha-community/koha-misc4dev/-/issues/76
*** Bug 37338 has been marked as a duplicate of this bug. ***