Funny you mention that I had the same idea; why is there never any discussion of this problem
Let's say the user wants to encrypt a file on her "smartphone" (portable computer bundled with a cellular phone)
Using her own choice of open source encryption program and her own key(s)
Are there even any "apps" that do this; theres an app for that; not this time
AFAICT its easier to encrypt the file using a different computer running an UNIX-like OS then transfer the file (back) to the phone
From there it might be copied to someone else's computer, i.e., a "tech" (middleman) company's data center; this could happen, e.g., when sending "private messages" or when "syncing" with "cloud storage"
When the user encrypts herself with no tech (middleman) company assistance, only the user has the keys and only the user can decrypt
"But users will lose their keys!" - Big Tech industry enthusiast
