I try to add a Gmail account, and it adds a completely different old account

I got a new Gmail account. Meanwhile, I recently deleted an old personal Gmail account. But every time I try to add the new G Suite account, it adds that old one back instead (though it doesn't actually work).

I've tried so many things. Deleted all my settings files. Removed accounts. I deleted the old Gmail from Safari.

But every time I add a new work Gmail, it adds my old account instead.

Another thread on this topic said to boot into safe mode, and that would fix it. I'm in safe mode now, and it's still doing it.

I'm at my wit's end and have no idea what else to try.

Edit: another bit of relevant info. I have a 3rd G Suite Gmail account from another company. I removed that one and added it back, and it works just fine. It's this specific new account that seems to want to use the old, completely unrelated account.

Edit 2: I just realized it's doing the same thing on my iPhone. None of this makes any sense.