Building, integrating, or customizing apps and workflows within Microsoft Teams using developer tools and APIs
That “Turn audio on?” prompt usually means your meeting join state is set to an audio-off option (so Teams treats it as “join muted”), which matches Microsoft’s description that if you choose “Don’t use audio” you’ll “join the meeting muted.” To join with speakers on (computer audio) but your mic muted, use the pre-join controls instead of turning audio on after you enter.
On the pre-join screen, “select your audio source” and ensure it’s “Computer audio” (not “Don’t use audio”), then mute only your mic before joining by using “select Mic … to mute yourself.” This results in “speakers on, mic off” at join time without needing the “Turn audio on?” confirmation.
If Teams keeps defaulting to the wrong device after your Mac upgrade, set your external speakers explicitly in Teams: go to “Settings … > Settings > Devices” and pick the correct “Speaker” and “Microphone” (and optionally “Make a test call” to confirm). If your org manages Teams, note Microsoft’s caveat that “some audio settings may be unavailable depending on policies set by meeting organizers or your IT admin,” in which case IT should review the tenant’s “meeting policy settings for audio & video.”