Probably a stupid question but can you create a save mid run to load if you mess up. I still have trouble with the jump in chamber 8 and this would help me stop resetting runs all the time.

Yes, you can also bind a key to quick save and another to quick load so you don't have to go into the menu if you want to save or reload.

If you are running No SLA or glitchless, yes as long as you can theoretically do the same route without loading a save, and in SLA or OoB you can load saves whenever the hecc you want

For clarification the save you load must have been made during the run; you cannot set a save at that part of 08 prior to starting your run then load that save if you mess up. You must save each time you get to that part (and wherever else you want to make safety saves).