Is the layer that you want to use generative fill on clipped to a clipping mask? IF so, this would be why it is greyed out. Unclip, do generative fill, re-clip.

I have a problem that I think many of you suffer from, which is Generative Fill is grayed out did all the solutions that are here and did not work
1- I registered my date of birth in Behance, I am over forty years old
2- I logged out and signed in Adobe Creative Cloud a thousand times
3- Install the latest version of Photoshop Beta
4- I deleted Photoshop beta a thousand times and reinstalled it
5- I talked to support in Adobe and I did not find a solution for them
I have works that the client must receive and I could not deliver them
Do I find a solution for you? I'm tired, I'm going to lose my job.

This is system information.

Adobe Photoshop Version: 24.7.0 20230607.m.2200 b619f20 x64

Operating System: Windows 10 64-bit

If you find that Generative Fill is greyed out for you, it is possible that you may not have a valid Date of Birth associated with your Adobe ID account. To update your Date of Birth, you can do any of the following:
• Log into Behance with your Adobe ID and enter your Date of Birth.
• Log into your Adobe account and enter your Date of Birth. To learn more, see Error: "Not eligible to use Creative Cloud services".
Once your Date of Birth is up to date, relaunch the Photoshop (beta) app to enable Generative Fill.
https://helpx.adobe.com/photoshop/using/generative-fill.html

Be aware that if you have previously entered a DOB and you are underage, the date cannot be changed. If you have not previously added age verification, and cannot enter your age verification via Behance, Adobe Customer Care can assist you. Go to https://helpx.adobe.com/contact.html and log into the site. Click the chat pod on the bottom right and type AGENT to get a real person who can help. Be patient 1:1 customer care puts you in a queue. Or you can reach out on Twitter at AdobeCare