I just noticed this is happening to me as well in the last couple of days. If Teams is open, but minimized it will change my status to idle. I then have to click into Teams and move the mouse around to change it back to available. It doesn't matter if I'm
actively working on my computer or not. I've tried manually setting the status to available and it does nothing. There's also no setting to prevent my status from ever going idle. I don't understand that one. I prefer to manually set my status as I use both
the desktop and phone app.
Whatever this last upgrade was caused a lot of issues with the app on my phone as well. I'm sure Microsoft is pushing upgrades fast to keep up with the WFH demands, but they really need to make sure they're giving QA time to test these first.