Comment by black_knight
7 days ago
This problem was solved by Plan 9 (roughly 1990) where there was a compose key to turn sequences into Unicode characters. Say compose-f-a to get ∀. This was all configurable in /lib/keyboard.
On so-called modern X11 or Wayland based systems (Linux or *BSD), there is a similar feature called XCompose. Worse syntax, but still functional.
Being able to configure your system to type the characters really doesn't solve the problem. In particular, if you get data (including metadata such as filenames) from someone else, you need to recognize the characters, both to do the configuration and then actually type them. And characters are not glyphs. There are all kinds of cases where simply looking at something doesn't and can't tell you what characters are in it.
And just to point out that there is WinCompose, for Windows, and a somewhat janky but usable solution using Karabiner Elements and macos-compose for Mac.