As a former imbiber of the Macintosh Kool-aid, I can attest that on a PC there is lot of junk going on under the hood that is better looked after for you in MacLand. It could even be that AE is not releasing and the last instance is still using ram. (on a PC you can have multiple copies of any app running at the same time)
Use cntrl/alt/delete to check the task manager and see what’s running right now (like another instance of AE). For “computer speak” items in the list you can search the web and it will tell you what those are and what they do. You can kill any process you want jst to try things out. That may give you more trouble than you would like as that process may have been important but they will all come back after a restart.
Also go to the start menu and type msconfig. This is kind of like the task manager but schedules processes to fire up on boot. So many machines (HP I’m speaking to you!) come with software installed that is supposed to help you manage the machine but instead end up gumming the works. You can turn these off to keep them from coming on at boot time. (hint: sort by manufacturer because most of microsoft’s stuff, and its going to be the bulk of the list, need to be there – except Defender which should be off if you have your own antivirus app: this alone can cause huge slowdowns as the two applications duel thinking the other is virus).
Also check software that loves to update itself (acrobat is nasty for this, as is citrix). It can take huge resources to constantly go out to the web to see if there is an update available and then start installing it when you least expect.
You can turn off many of these updaters in the MSCONFIG.
All adobe products are ram hogs (they need to be) but that memory is rarely managed well by the application and that can slow things down and even slow down apps you fire up after you have shut down AE. Get used to hitting purge all while working and when you exit AE, to clean things up and speed you along.
Using SSD’s can speed things up as well for the disk caches and source files.
Finally it could be the application fighting with how it has to output to your monitor{s}. Color space, size and frame rates can all affect how smoothly the running image is sent to screen. We have an Nvidia GTX 980 that shreds the image on the screen during playback and causes uneven frame rates. We have one that doesn’t. So there are lots of places this could be happening.