Does anyone know what the requirements for an ISA approval are?

I do at a high level and manage ISAs from the other side. Each ISA has a set of credit criteria to pass, and it's not at all just based on score. Each ISA is different but all the ones I see consider a minimum score as one of many criteria. You can have a great score but have too high of a debt load based on your current income, or have too many educational loans, or have other current ISAs, or have gone bankrupt in the past (which would probably ding your score), or have defaulted on loans before, and many many more. So I wouldn't overthink it but those factors you mentiones might impact your ISA even if your score is at the minmum. That said, even if you don't pass the credit bar, a program might still offer you an ISA, they are not regulated financial instruments with a bunch of hard rules.

You should look into loans from Climb, and Ascent as well. So all of these will run a credit check but you might be able to find something you are eligible for. Some programs with ISAs will accept you even with poor credit, the thing is if you have poor credit, they won't be able to get loans using the ISA behind the scenes so they can pay for your training before you get a job, so in the current climate not a lot of places want to take that risk.