1. Open archive.org and enter the channel link.
2. Select the saved copy before 2021, if available.
3. Go to the source code of the page (press Ctrl+U).
4. Find the phrase "plus.google.com" in the source code (press Ctrl+F).
5. If the phrase is present, then copy the GAIA ID consisting of numbers, for example 118427901813064144188. If the phrase is not present, then look at later copies of the channel in the archive.
6. Paste the received GAIA ID into the link:
7. Click the invite. Sign in with a fake account if you don't want to be spotted. Although it is quite difficult to find the invitation because it ends up in spam.
8. Also open Google Chat.
9. You get the email address of the owner of the YouTube channel
1. No GAIA ID.
View later copies of the channel in the archive.
2. Error in Hangouts.
This means that the GAIA ID belongs to the channel, not the account. Try to view the ID in other copies of the channel in the web archive.