Hi all. A heads up (and yes, I know it's my fault for trying) but in the MacOS Big Sur Public Beta, Illustrator crashes on save when Dropbox is open. After quitting Dropbox, I was able to Save As (an overwrite of the .ai file) but not Save.
Sorry to hear about this trouble. When you save and open files across a network or from removable media, many variables affect application performance. Illustrator does not support network or removable drives as scratch disks, or folders of file sync services such as Dropbox, Google Drive, and icloud.
As Monika mentioned above, we are still testing and optimizing our apps for Big Sur and don’t support it yet. We recommend that you use our apps only in released versions of macOS. For more details, please refer to this help article.