I have the very same problem and it driving me crazy. Incoming call notifications have a sound but not for chats. I was thinking I am the only one
You have Microsoft Teams version 23285.3809.2525.961.
You've got the latest version. It was last updated on 17.11.2023.The client version is 50/23101227712.
I have to admit I may have found my issue and I cannot prove this was always the issue from the beginning ... but I realized I was using MacOS/iOS focus mode most of the time. while working I was using focus "work" and with old Teams (which is now Teams classic) I had configured an exception for notifications during focus time. After updating to Teams 2.0 (and the renaming of Teams to Teams classic) this focus mode exception was still looking into a no more existing Teams app.
Since I realized this I now allowed Teams 2.0 to notify during focus mode and voila ... I have notification sounds again. shame on me ...