My old music player on Windows (MusicBee) had a way where it could sync music files to a storage device (in this case android phone) and convert lossless files to mp3 as it was syncing.
I’m trying to use SoundKonverter to do this, however the moment I hit start, it locks up.
Nothing that I know of from the top of my head does this under Linux, but as the previous replies have shared, there is plenty of software (GUI and command-line) to convert multimedia files.
If it’s imperative that the software can convert audio while it syncs to your Android device, you might want to look into the different offerings of media/music players, such as Strawberry, Clementine, RhythmBox, and etc. (There’s a lot of option, and some even have additional plugins you can add.)