I have been facing similar issue since last week, the network seems unstable as it switches to 4G and 4G+ often and stays on 5G for very short time.
and even if 5G is working fine and giving good speed, the phone suddenly drops the network for few seconds and switches back to 4G. And then doesn’t switch to 5G even when I select it from the settings.
It was working fine prior to this. Don’t know what’s going on, if carrier has an issue why would the phone drop the network, other devices on same network and same area works fine.