Ok, there is a lot going on in this thread. I have recently experienced all of this in the last 3 weeks so I will share my experience.
1. - My WifiRanger Osprey router did come with an AT+T/Winegard SIM. I purchased this router because it is compatible with the Winegard Air 360 antenna. And side note, WifiRanger was bought out by Winegard in the last couple of years.
2. - I purchased a FreedomGo data plan from Winegard and it worked, but was super expensive so I looked to switch.
3. - I've read a number of posts where people have said that they used a Verizon SIM in their WifiRanger Osprey or Winegard 1000 routers, but when I tried to order a SIM from Verizon the Verizon site said that my device was not compatible.
4. - I ended up with an AT+T Pre-Paid data plan. Problem is that the Winegard/AT+T SIM card was NOT compatible with the AT+T Pre-paid Data account, so I had to go to an AT+T store and get a new SIM. Fortunately that was free. But over 3 hours of my life that I will never get back!
5. - I FINALLY got my router to work with my new AT+T Pre-paid data plan using the new SIM.

6. - If you could see your VZW hotspot on the list of wifi sources on your Roku, then you should be able to connect your Winegard router to that hotspot. You would need to get on your laptop, log in to the router control panel, scan for networks, and then add the network as a wifi source in the Set Up screen. It should not matter than your phone is 5G and the Air 360 is 4G.
7. - In terms of router set up, you 'should' be able to connect your laptop to the router via wifi without having an internet source using the local IP address to the router control panel. You should then be able to then use the control panel to scan for wifi sources, and/or set up the SIM card. Note, you will need internet access to activate a SIM card, or purchase data.
8. - Regarding the xfinity issue. What I am reading is that the OP has a home xfinity internet plan that allows you to access mobile data via a hotspot BUT requires you to log in to their xfinity account to verify that you are using your home account for mobile data. While that statement may be confusing to some it makes sense to me. But that should only require the user to be able to access the internet from a mobile phone, along with their user name (or account number) and xfinish home password. I don't have xfinity so I would say that the OP needs to do more research with xfinity customer support on that one.