The "pseudo ROS" firewall rule won't do anything. Broadcasts are not routed between different router interfaces (which is where chain=forward works).
I'm not fluent in edge-ish, but I guess you would like to disable connection tracking for certain traffic. You can achieve that by rule something like this:
/ip firewall raw
add chain=prerouting action=notrack dst-address=255.255.255.255
which will instruct connection tracking machinery not to track those packets. If you want to do something about those packets later in firewall filter, then note that connection-state of those packets will not be known ... it will rather be "untracked". Beware: default firewall config has rule which explicitly allows untracked packets (part of "action=accept connection-state=established,related,untracked" rule).