Lots of issues with my new Series X

Hello again Johnny, if you tested with your smartphone's hotspot, and it worked perfectly, see if you can request some technical review on your network with your internet provider (ISP) may be that some configuration on your Modem/Router.

Try also to see if there are more people with the same problem with the brand and your equipment, it's an attempt rather than sending your console for warranty.

Thanks for your info, Onyx. Didn't want to send console for a repair but after all this I'm afraid I'll have to...

Thanks for letting me know. In this case then I think you may need to send the console in for repairs. You can set this up at https://account.microsoft.com/devices. Once set up and you have received your shipping label via email you can pack up the console. Please be sure to only send the console and nothing else as Xbox does not guarantee that extra items such as cables or controllers will be returned.

Hello, first it's a pleasure to be able to help you today.

My name is welcome to the community.

Hello JohnnyVolta, as you try "multiple solutions: Wi-Fi, Ethernet, DMZ, Google DNS, hard reset, factory reset mantaining apps & games, wiping all data etc"

Have you tried connecting your console to another internet network, other than the one you use on your home network?

Hey guys,

tested a few things in the past few days and I'm glad to say that my Series X is now fully working.

You could try the following if you're experiencing similar issues (this is exactly what I've done):

1. Modem/router factory reset - Performed a factory reset of my router even if it worked fine with all my other devices
   
2. Power Cycle your console - Turn off your console by pressing power button until the Xbox led goes off, unplug the cable and wait at least 10 minutes, then plug it back and turn your console on
   
3. Port forwarding - Even if my NAT was set to "Open" and my ISP reassured me that my internet connection was okay, I opened all ports required to use Xbox network. You can follow this guide (https://support.xbox.com/en-US/help/hardware-network/connect-network/network-ports-used-xbox-live) to do the same.
   
4. Success! (or at least I hope that all of this worked for you too)
   

Read online that many users used an ethernet switch to work around network issues. If you don't want to do what written above, you could try to buy one and test it yourself.

Thanks to all of you guys for the help!

Cheers!