How do I figure out what is inhibiting my screensaver and preventing lock screen/sleep?

At some point last month, I realized my screensaver (xscreensaver in this case) was no longer blanking the screen (and therefore also not locking it, and going into dpms idle/standby) at all. I had not changed any settings, but I did install nomachine in that time, which I suspected might be the culprit, but the nomachine server was disabled and that did not make a difference. Strangely, even when I manually locked the screen, after a few seconds of the screen being locked, it would prompt for my password to unlock, as if the mouse had been moved, and therefore dpms/standby never had a chance to kick in. But checking my mouse, and putting it on its side, and running xinput diagnostics eliminated hardware issues as the reason. Other questions ask similar things, but I figured I would create this question to compile what I did to solve my problem, in the hopes that it will help someone else. In other forums/questions, it is mentioned that this affects other things like hibernation and sleep, so hopefully this will give others a chance at solving this if they run into it in their use cases.