GarageBand is kinda tough to get fabulous vocals with. You can get good enough vocals with just a single vocal track and bit of stock compression and delay reverb. That is if it’s recorded well. That’s a whole other rabbit hole.

For mixing purposes I create a clean track, a reverb track, and a compressed track. For reverb use track reverb at 0% dry 100% wet. Copy paste the clean track onto it. Volume level set to where ever it needs to be nice and silky.

Same setup for compression and really compress hard. Same technique just bring volume up until you have a nice beefy vocal.

I don’t ever do much more than that to get good results. Best approach I’ve found