Teams on Linux is nowadays only available as a PWA you can install to your system through various Chromium-based browsers, though typically PWAs installed through the browser directly won't use the native titlebar, instead opting for their own window chrome. To get around this you can use something like Mint's webapp manager, which uses the native titlebar, or you can opt to use something like this community Electron client for Teams. I prefer to use the webapp manager since it also allows you to install extensions and user styles in the dedicated Teams chromium profile.
Microsoft Teams Default.colors
Microsoft Teams Dark.colors
Microsoft Teams High Contrast.colors
