I don't have a 2018 so my remote is probably different. The matrix unit is the HDMI splitter. It takes the output from various media devices, such as the satellite receiver, bluray player, etc and allows you to view any device on any TV.
This allows you watch your satellite on the Fireplace TV and Outdoor TV, and a blue ray movie on the bedroom TV. So you can show any device on any TV, even multiple times.
Mine as a set of A-D buttons and then 1-4 buttons. The A-D are the TV's and the 1-4 are the devices. I printed out a label and glued it to the back of the remote since there was no way I was going to remember the matrix

So I select C then 2 which for me means connect tv c (my bedroom) to input 2 (my bluray).
If you only have 4 buttons, it could be the remote is tied to a specific TV and 1-4 are just the inputs to that TV, or maybe you have to select 2-3 to connect tv 2 to input 3, whatever that is for your coach.