This isn't helpful.
I am experiencing the same issue right now, which affects my workflow.
My way of working with Teams is primarily with Focus Assist turned on - I knew about new message from red dot around Teams icon. When I wanted to receive also sounds and notifications, I was just turning Focus Assist off. Now I constantly receive these Teamsy blips about every message, despite the do-not-disturb mode.
It must be some update which broke this behavior - Teams now bypasses Windows do-not-disturb mode, which is unfortunate for a native Windows app.
My MS Teams are configured to use native Windows notification system. The computer was rebooted many times from that June 6th.
And it looks similar to CHK_1 case - with Focus Assist enabled, I only receive default Teams notification sound with every new message. With disabled Focus Assist - I receive Windows notifications *and* default Teams notification sound, so notifications are doubled.