I'm running both the Apple Silicon Beta version (25.4) of Illustrator and 25.3.1 via the Rosetta emulator, and having the same issue across both. Huge amounts of lag occur when double clicking an object to enter isolation mode. At first I thought it was because the file I was working on had a bunch of linked images, but now even new files with a single vector object drawn will have the same lag issue. A shutdown of the machine sees a new file operate as expected, until I enter isolation mode, and then the same issue occurs. Close that file, open a new one, and it's the case even with just the blank document.

It doesn't impact overall machine performance, and InDesign (Prerelease) and Photoshop (22.4.2) are working relatively flawlessly off the M1.