YouTube was the main platform for videos, but now Rutube is gaining popularity - many people moved here and started using it on daily basis since YouTube ban. Some libs are still mad and plan to use YouTube "no matter what", but they are the minority.
Other clones are Platforma and VK video, but they aren't so popular.
I also found the jitsi is the best for screen-sharing, it doesn't ruin the quality too much and doesn't overload your network