Per c:Commons:Village_pump/Proposals/Archive/2018/08#No_longer_allow_GFDL_for_some_new_uploads, except for software logos, diagrams and/or screenshots of GFDL-licensed softwares, any new files that are only GFDL licensed are no longer allowed on Commons at all.
Topic on Help talk:Extension:FileImporter
Yes, we should.
Only for new uploads. If the file was uploaded to a local wiki before 2018 I think it is still acceptable on Commons.