How many Red cherry shrimps can i have in my 20 gallon Long?

Hundreds. 200? 300?

No joke.

As many as you want, just be sure to keep up with water change and have a good filter.

You'll find out if you don't remove any
It depends on a lot of things. Filtration, food or no, water changes, etc.

Around 200- maybe 400. I am serious you can put a lot of them in there

Upwards of one million.

I once had 300 red cherry shrimps in a 10gal tank!

I had over 600 in a 10 gallon with 30 or more baby plecos at a time, did 50% water changes every other day.

I had 300 in a 3 gallon tank. Utilize all the space, put moss logs (with suction cups) on the sides, floating plants, etc. Shrimp like to bottom dwell unless you give them more ledges to hang out on. You can keep a lot more than you would imagine. I have about 200 in a 20 gallon tank right now and if you were to just glance in there you would think there are maybe 60. Until you realize can easily count 20 in about a 3 inch square area of the tank. I have 100 in a 10 gallon and could easily have 200-300 more and not be a problem.