I just tried this by doing:
$ ssh -X localhost
$ xterm # it launches
xterm$ exit
$ brave
X11 connection rejected because of wrong authentication.
[1]
I then strace’d brave and saw it was trying to access $SNAP_USER_DATA/.Xauthority, which of course did not exist. I then ran: $ ln -s ~/.Xauthority ~/snap/brave/current/.Xauthority, tried again and it worked.