Welcome to the forum.
There are plenty of star trail exposure time calculators available for the various guidelines (“rules”), such as
https://www.photopills.com/calculators/spotstars
Put the body on a tracking mount and periodic error is the more important obstacle to keeping stars round. On a tracking mount, 3 to 5 minute exposures are typical for each frame for cameras that have the ability to store longer exposures without over saturating the pixels.
For some camera bodies, a 20 second limit is a good idea, but that is more due to the full well depth size for that camera body rather than to prevent or allow trailing. 20 seconds for some bodies is the limit where brighter objects begin losing color by over saturating, turning the pixels white, especially when shooting in jpg instead of raw.