You probably can’t with 16:8 and omad. You could maybe do it depending on your size if you did a 20-30 day continuous fast or something like rolling 4-5 day fasts with keto refeeds. But I don’t recommend doing either if you don’t know what you’re doing.
It all boils down to what you put in your body. You can do 16:8 all you want but if you’re scarfing down burgers for 8 hours you aren’t gonna lose anything. Might sound cliche but have some damn salad!
Probs not I would do a 3 day fast then 16:8 for 3 days then OMAD for 5 days then cycle through that again personally (I may have misunderstood are you saying 20lbs a in 30 days? - if not yes you could slowly lose 20 lbs with ur plan) if so you need more fasting & to eat healthy & probs low carb ish during ur window & cut out alcohol