Q: Auto connect to 5G wifi band

Hello thebark4,

After reviewing your post, it sounds like you dont want the iPhone connecting to a different network. I would recommend that you read this article, it may be able to help the issue.

iOS and OS X: Recommended settings for Wi-Fi routers and access points - Apple Support

 

• Forget or remove the Wi-Fi settings for your network from any devices that connect to your Wi-Fi router. (This will prevent the devices from attempting to connect to your network with the old configuration.) You will need to reconnect these devices to your network once you've finished applying the new settings.

If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network - Apple Support

Reset your Network Settings. Tap Settings > General > Reset > Reset Network Settings. This also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you’ve used before.

Thanks for using Apple Support Communities.

Have a nice day,

Mario