The use case is not to do a search with æ or œ which always succeeds (if exact character exists) but to do a search with 2 letters : ae or oe and also find the one letter æ or œ .
I readily recognize that this request is superfluous because I only need to make 2 requests or instead of one. It's purely theoretical

Anyway thank you for your comments
For the fun (with my keyboard) :
œ => Alt. + 0156
Œ => Alt. + 0140
æ => Alt. + 145 ou Alt. + 0230
Æ => Alt. + 146 ou Alt. + 0198