I've had a similar issue, when my parents moved.
They got a working Smart Home setup, then they moved and got another router. Because no fiber was available and DSL with up to 4 MBit, they decided to take a LTE 5G connection. Stable, even streaming TV works ... But the Tuya light stripe and a cheap lightbulb cam won't connect. I tried everything, no errors, no timeouts.

I took the cam home ... Works in my lab. No issues. I build everything like my parents house, no issues at all. But I recognized they don't get a public reachable IP at WAN, some kind of CG NAT.

Now my parents got fiber to the home, with a real IP, and everything works.
But to be honest, do you want to have a cheap IOT device, that works only if connected to the internet by real IP? What kind of backdoor tunnel does it build up?

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