Hey!
Yeah, this usually comes down to the preview being too demanding for the system. I’d first try lowering the Preview Quality to Half or Quarter, especially when working with 4K footage or a lot of effects.
Also make sure your project and footage are on a fast drive and that your GPU drivers are up to date. If the lag only happens with one particular project, checking which effects/tracks are causing the slowdown can make a big difference.
Moreover, I am sure there’s been a similar question posted before, please, next time, try and search up the question using the forum search tool before actually posting it, thanks!