Yes, but I like to think the hacker community is persistent enough that if there were backdoors embedded in US or Chinese made hardware, it would have been found already.
Then again, they never found out about the Crypto AG communications backdoor (https://en.wikipedia.org/wiki/Crypto_AG) until 2018 as far as I know. Or they did know but since it's CIA they allowed it.
A backdoor could be introduced at any time by a software update.
Cutting off updates would leave devices insecure.
Do some devices not have remote disabling as a security feature?
A lot of devices and software store or backup to cloud servers.
Well, it took Juniper only 2 years find in 2015 the likely NSA implanted backdoors in their firewalls. Then the weakened Dual EC DRBG has been found.
Now (2023/2025) another two have been found.
Cisco equipment has been intercepted and implanted in the past.
So definitely "the community" can find things, sometimes it just takes ages.
And to add to your Crypto AG, Anom was also a nice example of the sting like this.