First, MoCA requires a PoE (Point of Entry) filter on the incoming line so the MoCA signal does not "escape" onto the outside line and cause interference with other cable subscribers on the same line. These filters are not expensive.
Antronix Filter, GLF-1002 MoCA "POE" Filter for Cable TV Coaxial Networking ONLY
by GoodFastDelivery
https://www.amazon.com/dp/B01EXRMIIC/ref=cm_sw_em_r_mt_dp_9zmdGbG6SRJDG
Second, MoCA network coax cables must "join" together via a MoCA compatible bi-directional splitter. These splitters can have a number of ports. To make sure the splitter is MoCA compatible, look for ones that support signals up to 2300MHz.
BAMF 4-Way Coax Cable Splitter Bi-Directional MoCA 5-2300MHz
by BAMF Manufacturing
https://www.amazon.com/dp/B017T9KF1S/ref=cm_sw_em_r_mt_dp_4CmdGbQCGY5EE?_encoding=UTF8&psc=1
Caveat: The more you split the signal, the more likely the signal will degrade and get weaker. You may have to add a MoCA compatible amplifier splitter to your set up to boost signal strength, especially if cable line runs are long.
PPC Entry Series Active Return 9-Port MoCA Amplifier Model: PPC-9M-U/U
by NetBetShop
https://www.amazon.com/dp/B076BK1F86/ref=cm_sw_em_r_mt_dp_wJmdGbFXZ85CP
Third, you need to terminate unused coax ports on amplifiers, spitters, and wall plates. Without termination, signals can generate interference on the line which can increase noise and potentially disrupt connections and network throughput. These terminators are inexpensive.
Coax Cap Cover, 75 Ohm Terminator, 10-Pack, RFAdapter, Coax Terminator Caps for Ports on Splitter, AMP, Coaxial Cable, TV Antenna, Wall Plates, Booster
by RFAdapter
https://www.amazon.com/dp/B07VWHX2FS/ref=cm_sw_em_r_mt_dp_uWmdGbF80YYCG?_encoding=UTF8&psc=1
Finally, here is how you can side-step the MoCA feature of your modem with another MoCA adapter. MoCA adapters typically have two coax connections and ethernet; one for passthrough and the other for connecting other MoCA devices. You can always try something like this ...
incoming coax --> moca coax port | moca adapter | passthrough coax port --> cable modem --> router
... then plug moca adapter ethernet into one of the network client ethernet ports on the router.
Your cable modem will send/receive signals through the passthrough coax port. Internal network traffic will flow through the router. With the MoCA adapter connected to the router via ethernet, internal network traffic will flow through the MoCA adapter to other MoCA devices. At first it seems counter-intuitive and circular but signals are separate and don't interfere with each other.
Don't forget... you'll need to install a MoCA PoE filter on the coax line in from the outside. Otherwise, the cable company will track you down ;-)
My current install has the incoming cable connected to the PPC amplifier (which has built-in PoE filter). Each of my coax runs connect directly to the PPC amplifier. In my home office, I have the above setup I described. Incoming coax into the MoCA port of the MoCA adapter and coax out of the passthrough coax port to my DOCSIS 3.1 cable modem. Cable modem ethernet to my router and then ethernet out of the router into the MoCA adapter ethernet port. Around the house where I need wired clients I have other MoCA adapters... coax into the MoCA port of the adapter and ethernet to client devices. Internal network speeds between clients on the MoCA network are as advertised. MoCA clients get near download and upload speeds of my Cox internet plan. Everything works like a champ.