Well, this is a question a lot of people have been asking about and I can say that studio lag can be caused by a lot of different variables. For one, if you have a lot of baseparts or parts in studio, they could all cause lag depending on your computer set up as to having a more powerful setup the less lag you may get from studio and games.
Another good reason you could be receiving lag in studio or in-game might be because you have a malicious file or plugin installed currently and it’s infecting your game with viruses which can lag a user in studio. This is something to be very cautious of because it could be multiple viruses or instances that are involved in this such as some being files you could have possibly downloaded or something from the roblox website directly.
I do suggest that you check your computers downloaded files, check your scripts in roblox studio, and close some things with task manager if it is your PC that is causing you lag in studio. If there are too many instances running on your PC, it takes up a lot of memory which can be slowing down your PC causing lag in games and studio.