How to revert to iTunes for AAC music downloads?
I would like to convert mp3 and wav to AAC format. Only AAC will download to iPhone now for offline use
[Re-Titled by Moderator]
iMac 21.5″, 11.7
Your title doesn't appear to relate to the body of your question.
See Convert music file formats in Music on Mac - Apple Support for details on how to create new copies of your tracks in a different format, should it be necessary.
Since you mention downloading to iPhone for offline use that would suggest that you have a subscription to Apple Music or iTunes Match. If that is the case you should find that both .mp3 and .wav files are capable of being match or uploaded to your iCloud Music Library, and then made available on your phone. They will likely stream or download as AAC content, but you shouldn't need to convert them yourself in your library first.
FWIW .wav files don't carry a tag and aren't an ideal format should they need to be imported to another library. Converting those to Apple Lossless might be prudent.
tt2