A Gain of Function experiment would do something like introduce a zoologic virus to human tissue.
Most of that bat virus won’t survive, but if some does then you now have a virus that will somewhat infect humans.
Do this over and over and at each step you are refining the virus and making it a more potent threat to human beings.
Rinse wash and repeat, and soon you have a potential plague.
This is old news. Those that were reporting g it last spring were ridiculed as conspiracy theorists. They were censored from the internet.