Did the WWE fans started to boo edge for the first time tonight?

I'm assuming you're just talking about his post 2020 career, but yeah hes a tweener now

For the first time, no.

Edge has been both a baby face and a heel at various times in his career.  So he has certainly gotten boos before.

As to why some fans are turning against Edge, the current character portrayal is shading him toward the heel side.  The current character is obsessed with winning the Universal championship and is willing to do whatever it takes to win regardless of who he is attacking.  At the end of the show, he was "setting up" to do a concerto on Daniel Bryan (currently acting the part of the earnest baby face who just wants a fair shot at the title) until he was "stopped" by WWE officials.  That will get you boos from the fans.

No.  There are no fans only computer screens.  The audio is created and piped out by WWE for the effect they desire. 

If it's a live event you will see some fans boo & some fans cheer just like DB 

BTW: HOF for the Jobbers