Hello Gustavo,
Welcome to Microsoft Community.
After fully reading everything you've posted, can I assume that you won't experience freezing issues if you use the Surface Pro 11 directly to play videos in full-screen mode without connecting to an external display?
So in fact I think you may have found the source of the problem, but from this information alone, it is impossible to tell why this exception is occurring. After a few queries on similar issues, I found this thread:
Win11 24H2: Fullscreen videos are freezing in all browsers, while - Microsoft Community
Customers report similar problems only occur with activated hardware acceleration and on different monitors.
This problem seem to stem from compatibility issues with the 24H2 update, which has been reported by a number of community users. So if you're still looking for some solutions, I recommend checking for updates in Windows Update as a priority. Some recent updates may be able to mitigate or fix the glitch you are experiencing. If the exception persists, refer to Shawn's reply message.
If there is any progress on the issue, please do not hesitate to share it here.
Best Regards,
Mitchell | Microsoft Community Support Specialist