I would like to lose them maybe in 2+ months. But as always the faster the better and its ok if I lose muscle too. My maintenence is 3500 according to the UD2.0.?
Let's do the math.
1 lbs of body fat equals 3,500 calories.
20 lbs of body fat equals 70,000 calories (20 * 3,500).
70,000 calories / 2 months (60 days) equals 1,167 calories per day.
1,167 calories per day is the deficit from maintenance that you require to achieve your goal. That is actually a pretty significant reduction from maintenance.
Notes:
1. Weight loss is generally non-linear. Rather, you will hit plateaus along the way. Seems to be a stair-step along the way, often stalling as you reach lower levels of BF.
2. No consideration is made for additional caloric deficit from exercise.
Also, you may want to rethink the "I don't care if I lose muscle" thing. The lower you get in BF, the harder it generally becomes to add it back on without additionally adding BF back on.
What is the reason that ud2.0 or a keto diet wouldnt be ideal for me or anyone of my size?
Because you should be able to get where you need to go without having to go as drastic as a UD2.0. You should be able to get there through energy balance/caloric deficit alone. Also, UD2.0 is a recomp plan, you are looking only to lose weight. (Although, I'd still focus on BF rather than BF+LBM.)
Generally, the lower the BF, the more difficult it becomes to lose BF without losing LBM. That's why UD2.0 is targeted to ~sub-13% BF.
Keto may work. I'll let someone with more experience take that one.