I managed to get all of my custom fonts to work with Word on my iPad by converting the OTF’s athttps://onlinefontconverter.com/ to TTF‘s. Then install as you normal would with AnyFont, iFont or what so ever.
I‘ve tried decompiling the .ipa of Word to get its included „office-compatible“ fonts to see wether they differ from „normal“ desktop fonts in version, identification, metrics, dimensions, encoding, unicode, other specific settings or with the kerning? I
couldn‘t tell.
I suppose it‘s getting just a little embarrassing for Microsoft not to be able to fix this issue many users — wether typography enthusiats or employees at companies with custom fonts — complaint about within one year of knowing.