I'm just going to copy and paste my comment in hopes others will see and understand the issue with the cinema game mode and the conflict of coding it relied on and how outdated it is now.

Adobe Flash hasn't had any real updates or fixes for years. Adobe has stopped supporting Flash protocol for a while now, and Flash will be gone by the end of this year or spring of next year. The Chromium Beta selection is obsolete now. Cinema needs a completely new coding system for YouTube, and I don't think that's likely to happen. Gmod cinema mode is dead unless Pixel Games makes Tower Unite open-source.

It's not worth the coding effort to make Cinema work with an old code for a game, because ad slots and new protocols and video queues have transcended. Pulling a video coding like YouTube wont work anymore. Trying to translate the coding and make it work with a very old game coding is worthless. Video protocol changes too often, and Cinema lasted longer than expected.

There are no more tricks or beta selections on running Gmod Cinema. You may find a few servers hanging by a thread, but Cinema is on its death bed.