So far, feature phones I could find are 4G at best. Though I definitely thought there'd be a market for connection sharing capable 5G feature phones. Am I alone?
It might be more fruitful to look at mobile broadband hotspots or whatever they're being called now. Could imagine a 5g one of those would be more likely?
And using a feature phone for security reasons is laughable. Feature phones are notoriously insecure.
If you need tethering, just use a 5G hotspot.