I have a keyboard 3G on v3.4.3 and the cell connectivity does not work anymore. It does still mention in the device info that it has 3G capability but if you try to do anything requiring a network connection it prompts you to connect to wifi. (Interestingly it also has the cell-style right triangle with five bars to indicate signal strength.)

I recall Amazon announcing a few years back that it would stop working; not sure if they pushed a firmware update, stopped paying the bill, or if 3G just isn't available anymore.

I dont think any of the providers around me still have 3g networks for it to connect to, and I know in the US amazon said they would lose connectivity in the US 2021

Yes, the connectivity should still work, but it might be limited depending on the model and the network you're trying to connect to. Some older Kindle models may have issues with newer Wi-Fi standards. It's worth giving it a try, though! You might also want to check if there are any firmware updates available for your device.