I unenrolled from the alpha skip ahead preview back when it 'bricked peoples xbox's

If you have unenrolled from the Alpha or Alpha Skip Ahead, the console will be marked in the Microsoft database for unenrollment.

However, if the System wasn't factory reset, the Alpha/Skip Ahead Software is still installed.

You might have to download an
OSUDT to an USB stick and do a factory reset with a fresh system install from USB.

Klick on the link above and follow the instructions for updating your console offline (the tile on the right).

I am with the Xbox Insider Program. But I cannot unenroll it because if I do, I can never return to it again. It's set to Xbox One Update Preview Alpha Skip-Ahead. I don't even know what that means since I am not a programmer.

Are you on the Xbox Insider previews? If so, they are changing it for something else. Can't recall offhand but it's in the release notes from a couple weeks back.

EDIT: here's the link: https://news.xbox.com/en-us/2018/06/18/new-preview-alpha-alpha-skip-ahead-1806-system-update-6-18-18...

You must be invited to become an Alpha Insider or Alpha Skip Ahead Insider, to do so You must Very active in Xbox, doing missions and report the bugs You see in the system, as much as You do this, so You Will be Very close to become an Alpha Insider. You
must be at least in Delta preview to become an Alpha Insider, but You Just need to be an Insider to be invited to become an Alpha Skip Ahead, but this one is very rare to be invited and there is a certain number of people to be invited, no more than that,
If You were not invited to be Alpha Skip Ahead certain time, so You must wait a Second chance when they Will invite New members.

If you're in preview alpha or alpha skip ahead, search for Xbox Game Pass Ultimate and you should be able to join.