Let's say, in our office, we used to take calls/meetings through Zoom & Webex. Usually, people say "Thank you. Thanks", at the end of the meeting. What else can we say in a polite and formal way? How would you respond in this situation?
The etiquette around online meetings is developing. One guideline is that you should mute your microphone unless speaking, and don't speak over other people. At the end of the meeting, it is confusing if everybody is saying goodbye so the best way to show you are leaving is to wave, silently.
The leader, chair or convener of the meeting can say something like "Thanks for coming, goodbye everyone". Everybody else waves and leaves the meeting.
In a one-to-one conversation, just say "Goodbye" or "thank you, and goodbye". A wave doesn't hurt either. Also smile!
But really, you are overthinking this. Providing you don't say something rude, it doesn't matter much.