Depends which split you like more (your plan to do first full body for 4-8 weeks is a solid plan, so you could do that). If you want to grow your glutes more, try doing glute bridge and hip thrusts.
Many people who go working out might not see changes, so try talking photos of yourself for progress picks, so you could see it more clearly if you truly have changed.
You could try doing recomp, which is normally done for 8-12 weeks. It helps lose weight slightly and build some muscle. I am unsure if lost muscle much but I think it's possible for you by the looks of it as beginner gains help out to do recomp.