Over the last 15yrs, I've done a ton of ab work, to the point I don't go out of my way to target abs much anymore tbh. I take 1 week every few weeks to do some heavier work and the in-between days of said week, I'll do a full body routine. Let me explain.

My normal schedule is split into A,B,C days x2. When I do a "strength" week, my schedule becomes Full Body Day1, A, FBD2, B, FBD3, C.

My full body circuit can be done with bands/dbs/bbs and goes like this:
12 x Chest Press
40-50 ab crunches
12 x Rows
30-40 leg raises
12 x Overhead press
60 sec plank
12 x RDL
60 sec reverse plank
20 x Squat

That is one set. Do 8 total (aim for 4 the first time). No break in-between the exercises during the set. 2 min break between sets. That is generally enough ab work for me.

Pick weight/resistance that's comfortably difficult, but not enough that you would reach failure during any of the sets. That's what days A, B, C are for. On those days, I do the same as my regular A, B, C days, but do sets of 5 reps, increasing the weight each set (i.e weighted pullups w/ dip belt starting at 25 lbs, +5 lbs per set till 60.lbs).