Just switched home network to T-Mobile 5G Home Network.
Everything in house works, including Nest Thermostat - BUT not my Gen 2 Nest Protect.
Thanks for reaching out and sorry for the delayed response.
I'm afraid that 2nd Gen Nest Protect sensors are only compatible with 2.4GHz Wi-Fi networks. Please check on this link for more information about it's technical specifications.
Checking back in — let me know if you still need help with your Nest Protect sensor.
Google Nest Help Center
Chromecast Help Center