Supplemental question

I am looking to do a few cycles with some supplemental lifts. I was thinking of running prep school but with both lifts one day I think it would be too much for what I have time for in my schedule. So I am thinking of running a 3 day FSL but with the 5x5 sets do a supplemental instead.

This is what I was thinking:
Squat day- Box squats
Bench day- Incline bench
Deadlift day- SLDL
OHP day- Close grip bench

Also I struggle with single leg accessory so would there be an issue with just doing Ab work all four days?

Why do you struggle with single leg accessory?
What are your current goals?

I am looking to drop some weight as one of my goals but also to keep pushing ahead with progressing in the main lifts. As for the single leg accessories I have a limited equipment home gym and my leg work is usually banded leg curls, which seems like they are worthless and just a way to gain a slight pump, and DB RDL’s. The DB RDL’s are ok but not sure how good they are working to build on the lifts.

Ok so injury is not the constraint.
I would do single leg work, you’re going to be missing out by just doing ab work 4 days per week. You could do 2 days single leg, 2 days ab or depending on total volume of accessory do 25-50 reps single leg and 25-50 reps ab which is something I tend to do for 50-100 rep targets.

If you have DB’s and BB’s you could easily incorporate single leg work you just need to be creative.
Zercher reverse lunges
DB split squats
DB Goblet Squats
BB Split squats, number of stances including rear or front foot elevated

Whilst not single leg are mentioned by Jim
Stiff Legged Deadlift
Good Mornings

They’ll be helping strengthen and build up hamstrings