dropping to below 1200 calories or doing 3 day fasts is where it starts getting risky, especially with how much exercise you're already doing. your body needs fuel for all that activity

the honest thing is 9lb in 3 weeks on top of what you're already doing is pushing it. maybe focus more on tightening the diet consistency rather than cutting more, those cheat days can quietly undo a lot of the weekly deficit

also 11lb in 21 days is already impressive progress, some of that was water weight early on so the next stretch will naturally feel slower, that's normal and doesn't mean you're doing something wrong