I am in a workspace with multiple admins. I want to make make myself the main admin, to have a space to work in with some others. However, when I tried it I noticed that I can’t make myself the main admin.
And I also can’t remove the other admins from access, because then it says that there should be at least one admin.
So, I guess this is a bug! 
I’m a little confused about what you’re trying to achieve, since you’ve talked about workspace and space.
Admin is a user role at the workspace level, and every workspace admin has ‘architect’ privileges in every space.
Workspace members (non-admins) can be granted architect access to a space.
There is a requirement for at least one admin in the workspace, but there is no such thing as the ‘main admin’.
It is possible that an admin can have his/her database access removed in a given space, but to do so requires that there exists at least one other user (admin or member) who is an architect in that space and has database access.
I already feared that may message may be confusing. With ‘main admin’ I mean the admin that has access to that particular Space.
If I want to accomplish that (and I am that admin), I want to:
If I start with 1, it warns me that there should at least be one admin & it doesn’t allow me to remove them.
If I start with 2, I type my username but I do not appear among the options. Only other users appear.
As a workaround, I assign another admin, they then remove the other admins, and then they assign me as admin and then they can remove themselves as admin from that space.
I hope that it’s clear now 