Xbox Series X, Wireless WiFi is connected, but not conneted to Xbox live. Phone Hotspot...

Have you tried restarting your router?

I have Xbox series x and I'm using a mobile hotspot and it only happens when I connect it to this hotspot. I've tried resetting my game and my phone

If the hotspot has a web-based authorization process you need to pass through (or a login page) upon connection to the hotspot, the Xbox cannot support that.

However, there is a workaround. You can try connecting to the hotspot with your phone, log into the webpage with your credentials, and then change the Wireless MAC address of your Xbox to the Wifi MAC of your android phone. Disconnect your Android phone
from Wifi as soon as you get them connected so you don't get conflicts.

In the Xbox network settings, go to "Advanced Settings" and select "Alternate MAC Address" to change your Xbox's MAC.

Hope this works for you!

is your xbox still configured to use wifi and to connect to your wireless network? if so then try to forget this setting and see how that goes, also you could try connecting it to a different wireless network to see how that affects things? ie temporarily
set your phone up as a wifi hotspot and connect the xbox to that and see how speeds are affected

Cheers

That is weird. Are you using your phone as a wifi hotspot and has Xbox connected to it?