For a long time, I’ve just put on DejaVu fonts and been done with it. Generally good enough Unicode coverage for me. But I know it’s been years since DejaVu’s been updated, and I wonder what’s very common today.
[As for the terminal, I’m guessing it’s usually still the standard fixed Unicode fonts?]
Ubuntu fonts works pretty good for me as a general UI font tbh. In text editors I prefer mononoki over monospace, it's a bit prettier IMO, although in terminal I use terminus because pixel fonts are cool.