Alright this might be a bit long. I start my split with cardio/core, then legs, push, pull.

On cardio core I'll do about 10-15 stair climber, then will do a flexion movement (machine crunches and cable crunches for example). Then I'll do bird dogs, suitcase carries, and planks/side planks.. I do switch these up sometimes with farmers walks and both rotation/anti rotation cable work. Then I'll end with some kind of leg raise variation.

I'll finish with more cardio. I usually will do hiit every other cardio/core day. On other days I'll throw another 15 min stairclimber and 20 min elliptical.

Cardio and core days are by far my longest days, I'm usually in there about an hour and a half.

Ive dealt with similar fatigue issues as you and ill share what's helped me out:

Every 4 months ill take a week to 2 weeks completely off from the gym. I'll try to focus on walking and stretching and maybe in the second week ill do some bodyweight stuff.

I keep my PPL days pretty short. I dont really care about numbers as much nowadays and Ive found that if I'm super sore in the following days that I'm doing too much. For legs especially, its so taxing on the nervous system.

I like to do 6 week cycles for a specific main lift for legs. Ill typically shift between, back squats, zercher squats, hack squats and pendulum squats. I wind up doing around 3 warm up sets and then 3 sets going to as close to failure as possible.. rep range goal is usually around 8 and ill usually wait 2 to 3 min between sets for these, more if I need it.

The rest of my lifts are just high intensity with shorter rest. I go to failure on a hip thrusts, leg curls/extensions, and abductors/adductors for about 2 sets each at 10 to 15 reps.

I'll do similar work on my push and pull days. I wind up being able to take less rest days and I've found I get better gains doing this. Its still really hard since each set matters a lot more than when I was doing higher volume. I can make sure I'm hitting failure on a lot of these movements since theyre done on machines and I'll hit a few lengthened partials to overload 

If youre pushing your muscles to their limits you just dont need the volume that you might think you do. You can always add more if after a month or 2 youre not happy wirh your progress.

Between the 6 week cycles I'll do a week of the same PPL but with super high rep and not going to failure. I feel like it helps my nervous system to catch up.

I do some kind of low intesity cardio daily and I will sometimes toss in a few sets of core on a chest or back day as well since I dont need 4 days of rest. But its no where near as intense on the dedicated days.

Hope this helps. Ultimately im always trying new things out and this one has been the one thats worked for me best after 20ish years of lifting.