Xbox app has me signed in as some random gamertag

That's odd
Could you try create a new local user on your a PC and then try on that new account to see how it goes?

Hi and thanks for reaching Microsoft Xbox gamer's community. My name is Josef.
I'm an Independent Advisor and a Microsoft Xbox user like you.

Hope you're doing great today mate

Please try sign out from your Microsoft account everywhere

Then try this:

Open Settings, click Update and Security and then Windows Update;

Click Check for Updates;

Click the Download and Install Now option, if available;

Also, check the Microsoft Store for any updates on the Xbox apps and its services.

Then do this:

Go to windows settings > apps > search for gaming services app > click on it and select advanced options.

After that, click repair and then restore.

Then do the same for the Xbox app:

Go to windows settings > apps > search for Xbox app > click on it and select advanced options.

After that, click repair and then restore, open the app and try again.

Finally do this:
Step 1: Open the Run window by pressing Windows + R key.

Step 2: Input WSReset.exe in the Run window and click OK.

Step 3: Then a command prompt window will appear. After a few seconds, Windows Store will open. Generally speaking, you can install or update the apps. If not, try other methods.

Done all that, deleted the Xbox app and then reinstalled it. It has a switch accounts button which when I click it says "Not you, I'll look around but doesn't come up with any other accounts even though Im logged into the right account on Microsoft. |So annoying

Hey, I have the same problem. When i sign in using my microsoft account on xbox.com it just shows a completely random gamertag that's not mine. But, i can't sign with my gamertag on my xbox as it asks me for my microsoft account, which is somehow attached
to some other random tag!

Hi, for some reason my old gamertag is showing on the xbox app, yet I changed my gamertag ages ago. Is there any reason why my old gamertag is showing on the xbox app rather than my new gamertag?

Try signing out and then signing back in.