Unless you’re 100% sure everyone will understand whatever acronym or abbreviation you’re using, don’t use them.
Acceptable always. Things like:
Acceptable only in specific groups where this is very standard terminology:
It’s not hard to type out the extra words. And if you really find yourself struggling to type all the letters, consider using text expansion, which automatically replaces text with longer versions. You can find this feature on macOS if you go to system settings > Keyboard > Text replacements
If you like this - and especially if you don’t - please also read Be concise