If I stopped doing IF and I stay under my BMR calories will I lose weight?
Weight loss is determined by calories in minus calories out. So yes as long as you’re under your caloric need you will lose weight regardless of what you eat or whether you fast or anything else.
All the dieting techniques out there only help you stay at a caloric deficit period.
So yes, you will lose weight. But you may be more tempted to snack, cheat, etc and accidentally overeat… so track every single bite!