There has been no firmware update for those hubs in quite some time. If it were me, I would go with the new mesh setup and also replace the ST hubs with either the V3 if you have Z-Wave devices or the Station if you only have Zigbee, Matter, and Wi-Fi devices. It seems as though ST is no longer providing any firmware updates for those hub models! @JDRoberts posted the below about changing the hub to bridge mode last year.
I think @h0ckeysk8er has those Plume models and may have more insight for you.