Right Click Not Working

Right-click is the same as Ctrl-click, so try that. It's indeed important to see if this is a problem that only occurs in Lightroom Classic or in all apps. If it's just Lightroom Classic then resetting the preferences will probably solve it. If it happens in all apps, then your mouse button may be faulty or you may use a special mouse with a special driver and the driver is not setup correctly.

While I think @Ian Lyons probably has the correct answer, have you actually ruled out mouse malfunction by right-clicking elsewhere (like in your OS) and seeing if it works?

Have you tried resetting the LrC preference file as described in Method 1 of linked Adobe Help document? Doing so often solves LrC misbehaviour.

https://helpx.adobe.com/lightroom-classic/help/setting-preferences-lightroom.html