You cannot join any beta without the container app. Go to the official Apple App Store and search for "TestFlight" (developed by Apple). Download it for free.
If you want, I can draft a ready-to-publish blog post based on this outline (500–900 words, neutral tone, SEO friendly) or create social share copy announcing an open TestFlight invite—tell me which length and tone you prefer. youtube beta testflight free
Here is the short answer:
You can often test new features directly within the standard app. Open YouTube, tap your Profile Picture > Settings > Try new features . You cannot join any beta without the container app
The YouTube beta is highly popular and has a (typically 10,000 users). If you click the link and see a message saying "This beta is full," you will have to wait for Google to clear out inactive testers or expand the limit. It’s a good idea to check the link periodically. If you want, I can draft a ready-to-publish