Bug

[Alison Porter]

Have recently updated illustrator to newest version 26.0.3 now Mac crashes. Using Big Sur 11.2.3. Is there a compatibility problem?

[Monika Gause]

Did you reset the preferences when updating?

This is often a good idea. You can try if it helps by renaming the preferences folder, which is reversible.

Other reasons could be corrupt fonts and certain antivirus (Trend Micro has been named a few times in the forum)

[Alison Porter]

No I didn't. Not sure I know what you mean. 
I did wonder if a file I was working had corrupted. I've stopped using that file. 

[Monika Gause]

When updating you usually can choose to migrate or reset your preferences.

The preferences are in your user folder. Locate them and then rename that folder (Illustrator needs to closed for that). When you next launch Illustrator, it will create a new preferences folder.

https://helpx.adobe.com/illustrator/using/setting-preferences.html

If you don't know how to handle your computer, you can also contact Cutomer Care: https://helpx.adobe.com/contact.html

[Alison Porter]

Ok thanks. I will check this out.