I’m going to guess that this is very much not true. For that to happen, every individual device would have to have an exploit that only China is aware of that gives them zero touch kernel level access where they invisibly install a rootkit that can’t be flashed off. Now, if you connect to a network and it says you have to install something first in order to connect, then all bets are off. I’ve heard of some exploits where this could be possible for specific devices running specific versions of firmware or software, but they are exceptions that generally can’t be replicated consistently in the wild.

I would say that if connected to a Chinese network, all of your traffic can be monitored, so a VPN would be heavily recommended.