@maxinm two problems, both most likely unrelated but potentially big:
1) your project filepath contains symbols/letters forbidden under networking rules
Please check the filepath in the top line of the last screenshot - do you see how each space has been replaced by an %20?
That is because networking rules forbid spaces in filepath and the browser can't handle them, it needs such an override to %20 to even function.
And unfortunately that override is not complete or perfect, and it will cause problems to your game. Please rename the project folder (for example replacing the spaces with _ to prevent those errors.
2) The filepath also shows that the project is stored in onedrive.
That is no problem for distribution, but never - NEVER - store a working project on any cloudsync'ed folder.
The RM's use databasing access for their files, NOT the regular filebased access. And most cloudspaces do not expect that, having been written only for regular file access.
As a result: if a cloudsync happens while the editor is working on the project, all project files can be destroyed and emptied.
It is rare because there are some protections to prevent that case, but if you search this forum you'll find dozens of topic where the files have been destroyed "failed to load actor.json" etc. And you'll risk the same if you work on a project that is stored in a cloudsynced folder.
As for your error - I'll give it a 30% chance that the option 1) above solves it, because it could be caused by the video plugin failing to load the video (the playtest works better because it intentionally redirects the filepath to a virtual one that has no spaces, just look at the filepath when launching the playtest)