So they don’t effectively block communication to and from the device? Or they don’t block all RF? Because the former seems to qualify as working, while the latter seems irrelevant. Or the only sometimes block communication to/from the device?

It is only irrelevant because devices made in this century put a lot of work into not transmitting outside of the intended frequencies.

My old Nokia would smash the whole range of AM/FM and UHF bands.

I don't know about higher frequencies that could escape one of these cages intended to block WiFi/5G/GPS but it is possible in theory and then it would be likely a backdoor that only becomes active when no signal can be detected.

> So they don’t effectively block communication to and from the device?

That is impossible to know without knowing the characteristics of the signal, noise, attenuation performance, sensitivity of the receiver, and other environmental conditions.

> Or they don’t block all RF?

They definitely don’t.

If you want to attenuate an RF signal, you need to do RF engineering. There are products to help people do this (eg RF test enclosure), but they aren’t marketed as “blocking RF” because that is nonsensical. The products that advertise as “blocking RF” without any real specifications are unsuitable for serious RF engineering, they are primarily sold to conspiracy theorists, hypochondriacs, etc.