I haven't looked at my config in a while. It appears I've got a single bridge, and ports get added to it with their VLAN tags (for ingress, I believe) -

    /interface bridge port
    add bridge=_bridge interface=sfp-sfpplus1
    add bridge=_bridge frame-types=admit-only-untagged-and-priority-tagged ingress-filtering=yes interface=sfp2 pvid=10

But then I also have to define the VLAN ID for the bridge (for egress, I believe) -

    /interface bridge vlan
    add bridge=_bridge tagged=sfp-sfpplus1,_bridge, untagged=sfp2 vlan-ids=10

The device is a CRS328-4C-20S-4S+RM. It seems like I am using the other recommended way. Which would make sense because I'm not really using the "router" part of the software, but rather configuring the built in switch chip to do its thing.

Looking at the text config now it seems quite sensible, and isn't far from SwOS, Linux CLI, or switch chip datasheets. But I remember getting to that point in the WebUI being somewhat confusing, perhaps due to the alternative in-CPU way you described.