I’m 29M, so my metabolism is probably slower than yours. I walk 12k steps a day and do 18/6 on weekdays, 20/4 in weekends. I am losing an egregious amount of weight while doing next to zero physical activity outside of work. Keeping your calories down is critical, I do salad and a fruit for lunch, and a serving of meat for dinner, and that’s it.
You have to ease into the fasting, i dunno how long youve been doing it but it takes some getting used to. When I first started fasting, I wouldnt restict my calories, I would just try to get into the schedule of 16/8. Soon enough your body gets used to the new routine and then you can start looking at the calories. But if youre failing at IF, i assume you mean you are breaking fast? I can imagine if you exercise a lot it would make you hungrier. With IF, you cant focus on the weight too much coz this is a really slow and steady process. Some people dont even lose any weight for ages and just drop Pant sizes like crazy and transfrom physcially. So focus on making the lifestyle change of only eating during these certain times by filling up on lots of healthy food, fresh fruit and water and dont beat your self up, soon the routine will come easier and then you can start controlling the calories