Don't think it gives you six pack abs but for sustainability (which is more important/functional) side planks and flat-backed bicycle kicks can go a long ways for core stuff.I am a full 20 lbs. down and am in a range where I am comfortable. I was looking at my Fitbit history and I haven't been this light in over 4 1/2 years. My wife said something about me being too skinny but I think she is crazy. I still need to work on my core and upper body and I admit I haven't done anything to get serious about it. Maybe if I add some muscle there it will change her thinking.
Congrats on the weight loss! Especially during the Covids.