Recent Apps button no longer pulls up the list of what's open on my phone. Had this problem BEFORE and you fixed it. I can't switch between apps or close open apps.

Thanks for reporting. Reports about the recents overview not opening are collected here: Recent apps gesture/button not working (In Review). Upvoting it gets you notified when its status changes, and one thread with all the reports helps us more than several.

Your form answer that Microsoft Launcher is fine is useful, because this screen is normally the system's rather than ours: third-party launchers cannot provide their own recents screen at all, which is why it often behaves differently as soon as a non-stock launcher is the default one (Recent apps screen & gesture navigation issues). That article also names a device restart as the one thing that sometimes brings it back.

Two details would help us a lot: which Niagara version are you on now (the form says "?"), and did the button stop working after a Niagara update or after a system update? You mention it worked again for a while, so knowing when it came back narrows this down.