There are 6 animations that i noticed this problem with.
One of them is when Kali gets aroused and slips you the "pill" , once mc starts f*cking her, animation is extremely fast. So fast that my eyes can't catch whats going on. I temporary slowed game down to 60fps via nvidia panel by forcing 60fps for that app , but thats kinda annoying to do. nvidia rtx 2080
From reading how renpy functions , i found out that it checks monitor refresh rate and then uses that to apply fps to the game if possible. That makes the problem. Animation is encoded for 60fps if fps is faster then video it produces triple the speed of animation
I have basically the same card, and don't have that problem, there must be something else causing it. Everything I see in Renpy is locked to 75FPS. Only time it was ever an issue was on a minigame in the game Bonerdale, made the last round nearly impossible for my crippled ass.
Your refresh rate and your FPS are NOT the same thing, and they really have nothing to do with one another, it shouldn't affect it. The FPS is how fast your card can throw the images out, the refresh rate is how fast the monitor shows new information. While they are similar in some ways, depending on how you think about it, and most things are better when both are faster, they are not connected. Your refresh rate should not affect your fps in any way, shape, or form. What the monitor can do, can't affect how fast the card is. That is like thinking that how fast you blink can affect how fast your car can go, you might not see it all, but it's still there.
I am not sure what the problem is, but I can say that it is not normal. I can't remember if we saw that issue before or not. You might want to check your drivers and codecs. You might also try another location, maybe even a slower drive (HDD not SSD). lol
Sorry I can't be more helpful here, I wish I could remember...
The only thing I can think of is to check your monitor settings, under screen resolution, if renpy doses somehow check and adjust to the refresh rate, a dumb thing for it to do, then maybe you can set it to something lower.