Playhead jumping and slow during playback

I'm having the same problem that occured around the exact same time as your post. My playhead skips to wherever my mouse is at the end of the scrub, but it won't actually scub. I also can drag lines on clips in the sequence, such as to adjust volume or speed up or down. It's incredibly frustrating. It happened on two project files that were working completely fine previously. I tried opening a new one, and the exact same problem is present. I have cleared my caches and reset preferences. Nothing.

Have you checked for an updated video driver specifically? The other thing to check (if it's applicable to Macs - I don't know because I don't have one) is the status of Edit>Preferences>General and then look at the Hardware Acceleration setting. If you have one, and it's off, then turn it on - and vice versa. Restart required whenever you alter this setting before it becomes effective.