Once you have licensed Copilot, you may find that the Copilot button is missing in certain applications.
I had this specific issue with Microsoft Teams. I tried accessing it via the web and it was also missing so I wasn’t expecting the issue to be anything to do with my Teams install, but I found this simple fix in a Microsoft community discussion page.
Deleting the following folder and restarting Teams fixed the issue and the Copilot button appeared.
%userprofile%\appdata\local\Packages\MSTeams_8wekyb3d8bbwe\LocalCache\Microsoft\MSTeamsHopefully this post helps you quickly fix the issue with missing copilot functionality.