Autokey (linux) or autohotkey (windows) as examples can do text expansion if you want to create custom symbols to expand to Or you could make a snippets progra

Autokey (linux) or autohotkey (windows) as examples can do text expansion if you want to create custom symbols to expand to Or you could make a snippets program in a terminal to copy a symbol to a clipboard (Workarounds I've considered since I don't have altgr or compose set up)