Most newer Mac’s (both Intel and M1) running macOS Big Sur seem to have performance issues in Studio. I have been able to reduce the lag in the script editor on my 2018 13-inch MacBook Pro by changing the color profile to the default color profile for my late 2013 13-inch MacBook Pro. It did not get rid of the lag entirely but the script editor is mostly usable for scripts with <800 lines. I mentioned the color profile change and also uploaded the color profiles and some logs on another thread.
I think that this partly being caused by Roblox Studio trying to access some system files that seem to be OpenGL drivers that were removed in macOS Big Sur. The main cause of the lag is probably that Roblox Studio is still using Qt 5 and Qt 5 is not optimized for Big Sur. Qt 5.12 (which is what Studio is most likely using) is supported on macOS versions 10.13 - 10.15 and macOS 11 is not listed on the supported platforms for Qt 5. Qt 6 has macOS Big Sur listed on the supported platforms and Roblox promised us that they will be updating Qt in Studio sometime this year.
Edit: Roblox Studio is using Qt 5.6 and I don’t think that they are going to update it to Qt 6. I hope that they at least update to Qt 5.15 because some other applications that use Qt such as OBS have recently been updating their Qt frameworks to improve performance in newer versions of macOS and I checked the Qt version for OBS and it said Qt 5.15.
I also updated my 2018 MacBook Pro to macOS 11.1 yesterday and noticed a 70-80% performance improvement in Roblox Studio (especially in the script editor). I am also able to edit scripts that are over 1800 lines long with almost no lag at all while using the default color profile.