Limit of one bridge per switch chip (able to be offloaded) is present since forever and I didn’t see any changelog entry which would announce a change.
No, it seems it’s a limitation of how ROS offloads bridge to HW.
OTOH there are only a handful reasons to use more than one bridge (where appropriately configured single bridge simply wouldn’t do) … so it might be you don’t actually need multiple bridges.
And any switch running SwOS (e.g. all CSS devices) work as if it was running single bridge.