Lightroom Photo Merge Greyed out

Hi Tom,

Thanks for reaching out. We're sorry for the trouble with Lightroom. We're here to help.

Could you please share the version of Lightroom or Lightroom Classic you are working on & the operating system you are working on? What type of images do you work with? RAW or JPEG? Could you please record a video or series of screenshots of the behavior you see & share it with us?

If you are working with Lightroom Classic, please ensure that the images you are trying to use Photosmerge are not missing.

Go to Library Module > Main Menu on top > Library > Find All missing Photos & wait for this refresh to finish.

Check this article if you find any images missing: https://helpx.adobe.com/lightroom-classic/help/locate-missing-photos.html

If you are working on Adobe Lightroom (cloud), please ensure the images you are working on have synced to the cloud first. Photos currently syncing might not work with Photomerge & Edit In photoshop workflow. 

Let us know how it goes.

Thanks!
Sameer K

What version of Lightroom? Lightroom desktop or Lightroom Classic? If Lightroom Classic then most likely the originals are missing.