Hi Andy, Not quite understand the "Workgroup", can you post a screenshot of it?

Can you post your settings page there?

Hi, as your other devices can work properly with Deco, you may contact Apple to see is there anything you need to do on the Deco router to make the Apple TV 4K to work. OlivierKlunder wrote More...

Is the LED light on the bedroom Deco green? Is that Deco connected to the main one by cable or Wi-Fi? So your Kindles are connected to the bedroom Deco's Wi-Fi, but no internet access or they cannot...

The TP-LINK support said a new firmware will be available on May or June

? Why is shows DSL info? MR3220 is not a DSL modem...... Check here, after login, you should be able to find the HW version on Status https://www.tp-link.com/en/faq-315.html