Several things to clarify.
Wi-Fi, whether it's regular old Wi-fFi or 6e or 7 or whatever, is localized. That means the RV needs to have a router somewhere in or near it for the wi-fi adapter to connect to. It won't magically connect to Wi-Fi if you are out in the middle of nowhere or driving down the high way. so not sure why you need an antenna to be placed in a window. That makes very little sense when dealing with Wi-Fi.
Unless you are parked in an RV park that offers Wi-Fi 6e, then that makes a bit of sense, but you'll still likely want to be parked pretty near the Wi-Fi router or repeater in the park as 6e is pretty short ranged anyway.
If the actual router is inside or on the RV, the external antenna is pretty unnecessary as the size of most RVs preclude any real issue with connecting to a router that is just a few feet away even if the Mac is in a cabinet. It's unlikely there would be any significant interference within the area of the RV.
Why are you connecting the Mac mini to a Tv from inside a cabinet? The Mac mini is not like an Apple TV you can control with a remote, so you will need to have a keyboard and mouse connected to it as well, and for that usually a desk is required, so the TV is not very functional unless you are using it near a flat surface for the keyboard and mouse.
With that said, many Wi-Fi 6e adapters should work on a Mac. Good reliable brands include brands like Netgear or Tp-Link.
examples:
click here ➜ NETGEAR Nighthawk WiFi 6 or 6E USB 3.0 Adapter (A8000) - AXE3000 Tri-Band Wireless Gigabit Speed (Up to 3Gbps) - Amazon.com
or here TP-Link AXE5400 WiFi 6E USB Adapter for Desktop PC (Archer TXE70UH) Tri-Band Wireless Network - Amazon.com
