I don’t use tags. But for those who do I think a tag suggester or filter makes a lot of sense. I would have assumed it would already be in place to be honest.
I do use notes. Mainly for the occasional transaction when I want to record the specific purpose for later reference or retrieval.
I do have a significant issue with notes and bank transfers though. It basically prevents me using notes with bank transfers and wish someone from Monzo could address it…