This is more likely a coverage issue than Walmart illegally blocking wireless signals (per to FCC regulations).
Report the coverage issue to Verizon and your local Walmart. Both of which will want to increase coverage of where people are gathering. This is because if bad coverage areas are in places where people gather this will cause affected people to switch services or stop going to those gathering areas if there’s alternatives.
I mean, yeah - fuck Walmart in general.
But I’m confused. How is Verizon’s misleading map Walmart’s fault.
OP might be inside a Walmart when they took the screenshot. Walmart either uses building materials that impede the signal or actively block it. I also can never get full 5G inside a Walmart, and sometimes I wonder if they are doing it on purpose to encourage using their local wifi. The only other time being inside a building messes with my phone is at the hospital, and I know they have a ton of equipment that could be responsible for that.