Audacity already has this: “Transport menu > Rescan Audio Devices”.
There is not a “simple button” but there is a simple command Transport > Rescan Audio Devices
There is no default shortcut for that command, but if you are going to use it a lot you can create a custom shortcut for it.
It can be useful for other Audacity users if they can find answers to their questions.
For future reference, please leave your original question(s) unedited on the forum for the benefit of other members of the Audacity community.