Switching from On Prem to 365 has been a non stop fight with Microsoft regarding implementing controls for admins. This is just another "Update" that causes the same thing. I feel like every ticket I've had with Microsoft regarding Intune, Exchange, Sentinel. Literally every single time it comes back saying "That functionality is not available please put in a request".
Then I come here to see there's already requests that are months (ifnot years) old. Then I go to find alternative ways to accomplish my goal to stumble across undocumented solutions from reddit.
Seems the public knows more about Microsoft's services than their "engineers" do and it needs to be remedied!
For this particular issue however, the answer is to just manually set it.. Which doesn't quite work because the OWA doesn't allow you to copy and paste pictures, or import an html signature, or anything else for that matter. You have to manually re-import the pictures and write the links yourself.