8 pack is genetic, I can get to 6 visibly when relatively lean (12%), if I was sub 8%, it would be an 8 pack but i've never been there or trained specifically for it but you can see one layer covered up. Maybe that's a goal for the end of the year. The 'genetic' part is whether you have that top 2 peaking below your rib cage or not. Just had knee surgery 5 months ago so I've got a layer of fat but if I tense, you can still see the 6 bulges as there is muscle mass there, minus the top two. I'll post a pic when I was 84kg (5"10) in a sec. Skinny abs if you are 65-70 kg, like big boobs on a fat girl, don't count.
Just train normally 3-4 days a week and in each workout, pick a rotary core movement, lateral core movement and 2 anterior core movements over the course of the week you could add one or two extra but I wouldn't go more than 3 anterior core exercises. These could be ab roll outs for 3 sets of 6-12 or dragon flags, maybe get-up sit ups but avoid too much flexion, landmines for rotary core and DB/KB mixed carries for lateral core. There are lots of other options.
You need the muscle, but you also need to be very lean. At least 12% for a six pack to to be visible without having to tense. Supplements are irrelevant.
8 pack does tend to be unrealistic, most people can get a good six pack if they work hard enough. Some can get an 8 pack - maybe 10%, but only if they are extremely lean and have the top two below their rib cage. Outside of the bodybuilding population, it's unrealistic tbh and probably not healthy to be that lean. You will be hungry at 8% body fat and that's why bodybuilders only stay leaner than that for a short period.
Full body routines, upper lower routines work the best... athletes use these and they are always the most ripped without being puffy. Squats, deads, lunges, single leg squats, split squats, push variations (push ups/weighted push ups are best for core), pull variations (chin ups work more core musculature), along with the core work... factor in sprinting, jumping and throwing the med balls and it all adds up. Build the muscle then strip the fat. You don't need to do silly core routines dedicated for 30 mins 4 days a week - that doesn't work - you need the whole body response from training properly and you're abs will follow. Work your core like you do any other exercise, but note that the role of your abs is for anti-extension, so don't flex them like crunches. Same with the obliques in rotary/lateral core exercises. This is a mistake most people make.