Not sure what you mean by "greyed out". Can you say more about what you mean? Can you take a screenshot, upload it somewhere (e.g., Dropbox or Google Drive), and provide a link here?

Have you used Zotero on this computer before? Are you running any third-party software that might be interfering?

First start Zotero from Terminal with the -P flag to see if the small Profile Manager window is also blank. If not, you can try creating a new profile to see if it still happens with that.

After that, I would try running it in a new macOS account to see if it still happens there.

Don't know how to run Zotero from Terminal

I linked to instructions.

That's not relevant. The question is whether you see the Profile Manager window.

What do you mean by that? What happened, exactly?

Can you share another screenshot that shows what you're running and what's happening?

Unchecked the 'use the selected profile without asking at startup' box and it now works fine. Thanks for your help

Unchecked the 'use the selected profile without asking at startup' box and it now works fine.

@Intensivist: That's not a fix, though. If you check that again and start Zotero normally, does the same thing happen?

Great.