User Cannot Edit Report

Guest users lose edit access often because they’re not switched into your tenant—they might be in their home tenant where editing is blocked. Make sure they explicitly switch to your tenant before editing.
Also, check your Power BI Admin settings for guest access permissions and confirm they’re accessing reports through the workspace, not shared links.

Hello Andyw54,

Thank you for posting your query in Microsoft Fabric Community Forum. Also, thanks to Shahid12523  , for those inputs on this thread. also check in the Power BI Admin portal that the option “Allow external guest users to edit and manage content” is enabled. Sometimes guests lose the edit option if they are still in their home tenant session, so asking them to log out and log back in to your tenant helps.

Kindly refer to the below documentation links for better understanding:
https://learn.microsoft.com/en-us/fabric/enterprise/powerbi/service-admin-entra-b2b

Hope this helps if you have any queries we are  happy to assist you further.
Best Regards,
Harshitha.