I can’t email a photo through Lightroom

Lightroom does not support emailing (with text) from within the app. You would need to Export the image to a local folder to be able to attach the exported image to mail in your usual Email application.

You could instead share a link to a single photo, or an Album of photos, and the link can be automatically emailed to a recipient to view in their Web Browser.  [Right-Click] on a selected photo and choose [Share & Invite...].

https://adobe.ly/3FTetM1

Lightroom will add the share to the left column of the Lightroom UI-

Or if you simply [Right-Click] and [Get Link] you can add this link into text in your usual method of emailing.