I just figured out how to remove the M365 Copilot annoying sign-up App from my Android phone. All of a sudden now, every time I tried to open a text file on my phone with any kind of extension, it would go straight to sign in page of M365 Copilot. I couldn't even choose what app I wanted to use to open the file, so I couldn't open my file, no matter what, unless I signed-up with this app, and I DON'T WANT TO.
Microsoft held me hostage to my options. Finally I found a way to get rid of this parasitical program/app and it's insisting spam. I must say as many here stated. This is pure hostile spam and criminal behavior to push their product like this and force people to use it without clear and easy options to make it disappear from their phone.
TO REMOVE M365 COPILOT FROM YOUR ANDROID PHONE:
Settings / Apps / Your Apps (in small print) filter on the right side / Show System Apps (slide switch ON) / OK / scroll down to M365 COPILOT / scroll down to App details in store / (this will open Google Play store) UNINSTALL.
Another way to do it is:
Go to the Google App Store, search M365 COPILOT and UNINSTALL
Then, take a deep breath and ENJOY your victory!