All of these issues you highlighted are because you ran 11 tabs on the same machine. It’s a miracle they even loaded at all… lol. You simply can’t do that - your resources take a huge hit.
Frankly, you just need to test with about 4 clients or so to ensure there are no connectivity problems. In ‘production’, users will be connecting from different machines and will (likely) be on different networks, so the lags and deprecation you observed in this test won’t surface. Frozen videos are a result of limited bandwidth. And just in case you didn’t realize this, Jitsi even gave you a clear message “Video turned off to save bandwidth”. So again, everything you’ve reported here is as a result of the limited resources you committed to testing.
Bandwidth (like CPU and memory) is like food. The more people you have eating from the same plate, the less each person will get. You can’t expect everyone to get filled from the same amount of food that feeds just one person… lol.