I have a custom solution with the Application Ribbon component which contains a few buttons, globally available on all entities in the system. This solution is deployed as a managed solution, and is self-contained.
Now, on my dev instance (which is, admittedly, bit old since it's the 2014 on prem CRM version) the buttons show up fine for all entities as expected. I can take this solution to a CRM9.0 on-prem instance with equally satisfactory results. It also worked for a customer using CRM 365 Online WITHOUT the Unified Interface patch.
However, that customer has now updated their online CRM instance and enabled Unified Interface, which caused the buttons to no longer appear. I've started investigating, and I was unable to create even a simple global button at all using the ribbon workbench (for testing purposes I've tried creating a button that just opens up a web page, with a simple enable rule). This was created using a new solution with the Application Ribbon component and after publishing the button was nowhere in sight.
Is there a new method for creating global buttons when using the Unified Interface? I really need these buttons to be global and while I could, as a hotfix for a select customer, just re-create the buttons for select entities, in general this isn't how the solution is supposed to work and the buttons MUST be global.
EDIT:
I've made some progress when it comes to analysis. I was eventually able to make a simple button appear - so global buttons as such ARE working (however, to be absolutely honest, I have no idea why my initial attempts failed).
I've also found there's a button checker tool which should help "debug" why buttons aren't popping up. Well, in my case, ALL of the buttons enable rules (no display rules) are "skipped", which isn't very helpful. This leads me to believe the issue might be with the action itself, but the action just runs a JS or opens a web resource (depending on which button we're talking about), so that's also not very helpful. Any idea what could be wrong here?