Just because the map shows you can get 5G (or 4G) does not mean you'll actually be able to use that network. It's tricky and telecom companies like to play these bullshit games. It's pretty similar to how they'll advertise "up to X MBPS" internet speeds but the average speed is far lower.

You'll actually have these experiences in congested cities. Ever go to a concert and realize you don't actually have cell service? That's because the tower is fully occupied. Unfortunately phones might not report this to you and might not report the downgrade. Making Android and Apple complacent...