I don’t have an account with classroom, I create a basic room. I was able to add/upload a pic to change the theme of the room I created without issue. We’re not stopping people uploading pics.
Uploading the picture, looks like a similar gmail file upload, which also works in Brave. Would test in private window mode with no extensions.
Thanks for sharing your experience but for me its only happening when uploading file in google classroom so far. Its quite annoying that I need to change web browser and take a lot of time.