After effects only lets me use a certain fps, and when i change it my audio speeds/slows

It might be your computer can only show 20fps and is not capable of anything faster?

Can you please share your system info? Like OS and version, CPU, RAM, GPU vRAM, Ae version? Thanks. Also a screen grab of your issue will be helpful.

FAQ: What information should I provide when asking a question on this forum?
https://community.adobe.com/t5/after-effects-discussions/faq-what-information-should-i-provide-when-asking-a-question-on-this-forum/m-p/3928960#M3238

Without any system iunfo and details about your project contents none of this has any meaning. As Warren already explained there's any number of ways to mangle the framerate and smooth realtime playback may not always be guaranteed, be it just for performance issues on weak or poorly configured systems, specific issues with your footage or more mundane stuff like another app on the system messing with resource usage.

Mylenium

The Composition Frame Rate is the frame rate of the animation.

The Preview Frame Rate is the frame rate of the preview.  That is, After Effects allows us to work at a faster or slower speed that the Composition.

When you see the frame rate in parenthesis in the Preview panel,  After Effects runs the Preview at the same frame rate as the Comp.

moving this to the AE forum

The Preview Rate in AE is just that...a preview.

when you Render it..it should Peview at assigned frame rate.