Hey @Beard_Greg, no worries - I appreciate your help! By the way, I fixed the issue. Turns out it wasn't a Power Automate issue or anything to do with the authentication. It was my report template. Somehow I tested it and it worked perfectly 3 months ago and revisiting it now, something was up with my syntax for one of the photos. Either way, so glad it is resolved.
My flow with the HTTP request actually directly uploads the created report to SharePoint, so it's an alternative approach to the method you show above. Here's my general flow: