it sucks when Apple gimps file sharing for everyone by refusing to use standards

Fixed it for you. If Apple supported RCS this wouldn't happen. But I guess you prefer to follow Tim Cook's monopolistic solution and buy them an iPhone /s.

RCS doesn't have a cross-platform end-to-end encryption solution. For cross-platform communication, cross-platform 3rd party solutions such as Signal work well.
What security issues does Signal have?
@RandomBit I'm not aware of exactly what issues #Signal has, but I know it's centralized so I'm not a big fan of that
Yes, it's not ideal. Decentralized key distribution seems to be a intractable problem for mass adoption.
Sort of off topic but are you replying from Mastodon?