The recent file history disables menu items when the referenced files are not found when Slicer starts. The missing files may be available again if they are on removable media. They may also never appear again and occupy space without purpose.
The only management option is Clear History The purpose of this feature request is to add a Purge History option, which would simply remove the disabled menu items.
Perhaps another Update History option also, which would refresh the menu items presentation if a removable media is available again.