When I have several audio tracks and I want to hear only one of them and mute the rest I would click the button “Solo” and Audacity then would mute the rest. That is how it must work, but instead you have to mute the rest manually. Mute button works perfect but the Solo button must do the mute to the rest of tracks.
I understand you decided it to work as it does because you would like to hear 2 audio tracks for example, but that can be made after click on Solo on one track, unmuting then the other tracks you want to hear too.
Also Ctrl could be used this way: When you click “Solo” it mutes the rest of tracks. When you hold Ctrl and click “Solo” it only puts that track as Solo without muting the rest of tracks.