A customer of ours is having an issue with SharePoint. Recently when sharing links from within SharePoint they've not been able to share them with edit permissions. The edit option is grayed out.
To allow the sharing of links with edit permissions I need to go into the library settings and modify the setting "Require documents to be checked out before they can be edited" to No which is under versioning settings. Once this is set to no, editable links can be sent.
The problem for our customer is when Require documents to be checked out before they can be edited is set to no, they are not enforced to check out documents. Which is the setting doing exactly what it should do, however they said a week or so ago they were able to send editable links out, and forcing the checking out of documents via the setting mentioned above.
Speaking to the customer they said they lost this ability in the last week or so. I've spun up a demo tenant and the same issue occurs for me.