Personally I would find very useful a "search only by tag" selectable option without alway having to digit the # as prefix, then It would probably be useful to also have a "Search only in filenames" , "Search only in text body" , "Search only in attachments" and "Search only by date"

Regarding tags, I know there is already the Tags element in the left panel but it is inconvenient for me to use. For some graphics projects I have notes with dozens of hexadecimal color codes listed and since they start with # they all get listed there because are considered tags.