Hello XinyueCao,
Based on the screenshot you provided, my understanding is you are using Teams desktop app on a Mac machine, please clarify if I misunderstand your scenario, thanks. If so, first please double check have you opened the Teams app with full screen mode or a bigger size, generally if the opened window with a small size, the Teams icons in the left hand maybe hided, so please try to make the Teams with a full screen mode and then see if you could find the 'Teams " icon there, thanks.
Moreover, if you cannot find the Teams icon with a full screen mode, in this case to isolate if the problem is related to your Teams account or the desktop app, in this case please use your account to sign in the Teams Web App and then see if you could find the icon there, you could access the Teams web via https://teams.microsoft.com/.
Please feel free to share with me if you got any further updates, thanks.
Best Regards,
Oliver