I have no idea how to do this, is it really that complex to get the drive back up and running?
when you start messing with permissions and other advanced stuff, then yes it can get complicated real quick. looking at the blurry video you got to the security window and there are no users listed with any permissions at all. this is why you can't access anything.
from there you went to the advanced window and to the "add user or group" window. that is where you need to start adding users back if it will let you. start with the "administrators" group. give that one full control if you can. this will allow you to get to all the files assuming your user is an administrator account.
then add the "users" group and give them everything but "full control" and "modify"
then don't mess with it anymore until you know EXACTLY what you are doing
there are a ton of other users and groups but for now those are the important ones and should get you back into your files.
as a side note, the "administrators" group and having yourself as an administrator is not the same as the built in Administrator account which is disabled on win 10 by default. this is a common point of confusion for novice users. putting yourself as an administrator gives you a lot more access to the system, but the built in Administrator account has almost limitless access which is what makes it so dangerous to use day to day and why it is disabled by default.