It’s pretty easy to disguise your accent/dialect when singing. Many bands have done this. It’s when you hear their dialect that they are actively trying not to cover over it, IMHO.
When Tom Petty and the Heartbreakers came out with Southern Accents, you’ll get what I mean. It was deliberate for that song.
ABBA could write a book (or a song) about losing one’s native accent while singing in a different language.
Sometimes, one cannot get rid of the accent, or doesn’t even try. In the song 99 Luftballons, I could clearly hear Nena’s German accent. I thought it added to the “Worldly Gypsy” credibility of that song. That quality helped it to sell.
The Beatles certainly sounded American, without so much as a hint of their native accents when they were singing, and the Rolling Stones sounded like they hailed from somewhere south of the Potomac.