There is perhaps another way of seeing things. I spent some time today working on a KBM macro to add tag as you suggested, only to conclude that the best method (IMO) is to select document → ⌃↵ → type in tag. With any other method using BTT or KBM you forfeit the HUGE advantage of / Live while typing and / Partial matches while typing, and will probably end up with multiple pseudo duplicate tags like covid, covid-19 and coronavirus
I would tend to take the opposite view and stick to DevonThink whenever possible. That being said, I have probably 200 DevonThink Keyboard Maestro macros.