Maybe your on old firmware? modem mode is said to be removed on newer firmware because VM want everyone behind there NAT and trying to make out Ohh no with fibre we must do router when really they just want active Statistics that cause ping drop and spikes.
Its said that modem mode may work on 1Gb ports the top one as 10Gb port may not work the only other way is to search betterinternet SFP+
VM my also want to see your devices with there O so good NAT router but you can just double NAT so they only see one device then you have to port forward or DMZ to it which they don't support and them say we only support upto the hub yet BQM is to the hub and they don't support a stable ping with all there auto speed tests they do.
In short Docsis is better till they add modem mode on the 10Gb port for fibre I mean IP pass through is another way I would be happy about being its only limitation is change your MAC to get a new IPv4 but aside from that just like modem mode with your WAN IP to your router and even VM can do their Statistics.