In which way exactly does things break for you? If your management access breaks … then it’s because you’re setting BR1_interface_ as tagged member of “default” VLAN (VID = 1) while corresponding (untagged) interface doesn’t exist (and even winbox can’t talk to ROS without appropriate untagged interface). You can get a suitable interface by running
/interface vlan add name=vlan1 interface=BR1 vlan-id=1
Or you can leave BR1 port untagged (by not adding it as tagged member of VID 1 … setting of pvid=1 on all bridge ports, including BR1, is implicit default). More on various bridge personalities.
The configuration commands from attached file seem fine. Now please also post exact configuration after the commands are applied … execute /export file=anynameyouwish, fetch file to admin computer, obfuscate any sensitive data (using any text editor) and copy-paste contents here.