You can see 30 generations if you pick someone in the middle of the tree. I did some playing around with the settings and screens size, and on a 4k, 32 inch monitor, you can just barely read the names with 30 generations. If you display any other information (like life years) then you can fit about 23 generations on the screen.
What is your use case that you need to display more generations on the screen at once? How many generations do you need to display?