The switch will not move
Two completely different causes that look identical. Up to macOS 12 there is a padlock at the bottom left, and while it is closed every switch springs straight back without macOS explaining why. From macOS 13 the padlock is gone; a switch that stays stuck there usually means the Mac is managed by an employer.
Applications
Apple menu, top left → About This Mac — It shows the name there, for example "Sequoia 15.6". From macOS 13 onwards this window looks different than before.