SashaMars we have some customers that are big users of M365 and Azure, and others that are primarily M365 with minimal Azure.
Ideally there would be a "branding management center" in each cloud that was synchronized/shared resources. It would be good to be able to have a single branding asset, that was targeted at many different UX options.
Clients also need to the ability to customize notifications/emails/mfa prompts, these need to be spoof proof and tamper resistant.
I can imagine a wizard that walks me through some choices about where I want a logo to appear. ideally the same graphic would be processed appropriately to display correctly in different resolutions, screens, devices and themes, or we could have a collection of images that would be targeted accurately. We should not have to do trial and error testing :).
Let me know if this helps or you have any questions.