You can access debug mode any time, which you can learn about [here](https://youtu.be/NTWC2YxeCH0). Go into any game in Anniversary Mode (except Sonic CD) and spawn a bunch of coin boxes. Then you can buy out everything in the museum right away. It’s a damn good feature by the developers and perfect for if you just wanna see all the museum content.
Edit: I just removed a part in the original post that called this whole thing an “oversight”. And after experimenting with it myself, I don’t think it is. I’m completely convinced this was 100% intentional by the developers. So have at it!