+Additional context, following the same instructions on my ADM account. I do have the ability to "Create connection", but once again I can't find existing connections.

This is odd because (A) I should be able to leverage existing connections and not need to create a new one every time, and (B) both my ADM and regular accounts have the same access as far as I can tell.
... Wait, this is EXTRA WEIRD (writing in real time). I see my existing connections now after refreshing the page!

... Likewise, I went through the same steps on my non-ADM account. Originally, it came up just like I described originally (no existing connections came up). But after I refreshed the page, IT CAME UP!

Not even sure what to call this, but this seems like a genuine bug.