3D & Materials window refuses to open 2019 16 MacBook Pro

Hello @Gareth W,

Sorry to hear about this experience. I hope the suggestions shared by Monika helped resolve the problem. If not, kindly try resetting Illustrator's preferences manually by following these steps and check if that helps resolve the issue:

For macOS
• Close all Adobe applications.
• Go to the following locations
• ~/Library/Caches
• ~/Library/Application Support/Adobe
• ~/Library/Preferences
• Rename Adobe Illustrator, com.adobe.illustrator and Adobe Illustrator 27 Settings folders to Adobe Illustrator.old, com.adobe.illustrator.old and Adobe Illustrator 27 Settings.old
• Launch Illustrator from the Creative Cloud.

Note: Location starting with this "~" sign indicates the User Library, which is hidden. So, you need to copy & paste the exact path in spotlight search or from Finder Menu > Go > Go to Folder > Paste the location in the dialog box like this:

Disclaimer: Please note that renaming preferences folders will remove all the custom settings, and Illustrator will launch with default settings. You can also save a backup of the folders in case you want to. The location is mentioned above.

Looking forward to your response.

Thanks,

Anubhav

Please tell us the specifictions of your mac. Especially the amount of RAM.

But also: please check Edit > Color settings. If it is set to "Emulate Illustrator 6", then please turn color management on and set it to something that makes sense for your place of the world (it's actually region specific - the region where you send your work to print).