Searching is not done by Picard but rather by Musicbrainz.
See this recent thread for a similar issue, and bug diagnosis.
As far as I know Adele has never called herself Adèle, however I have added this as a search hint (since a French speaker might spell it this way if they didn’t know better), so when the bugs identified in the other thread are fixed, this should work in Picard.
I stand corrected - there is a difference between aliases and diacritics. More research needed.