I dug out an old Acer Aspire E1-771 laptop and put Ubuntu 18.04 LTS amd64 on it (just Ubuntu, no Windows). I now find I can use Alt + X to insert Unicode sequences even though I thought this was impossible. I am transcribing an old chemical document and can enter all the Unicode characters including 5-character ones with the letter F from a standard external keyboard without NumLock and without case sensitivity.
I cannot do this on any other machine running Ubuntu 18 or 19 (I have half a dozen computers).
I'd like to copy this feature to the other machines if I can find out the underlying mechanism.