Most people here are referring to transfers of their own data. How do people transfer their confidential information to say, their solicitors, who may be on different operating systems and behind NAT / firewalls?
Specifically if cloud services are banned by the solicitor's company.
You'd have thought by 2023 this would have been solved but I don't believe it has. Particularly as PGP email administration (including key management over time / replacement hardware) is non trivial and unlikely to be successfully achieved by the non tech savvy.