I don't necessarily want email and calendar bound either... I was just trying to use it to get off Google.
After commenting here I went and found a enhancement request re: the same issue and left disappointed comments. https://github.com/tutao/tutanota/discussions/3067. Unexpectedly, they closed the issue and explained that it's been fixed for a while. I posted a screenshot to show no custom options were available and they explained the drop down was scrollable and there were more options if I scrolled down. There's no UI element to even hint that it's scrollable on mobile or desktop, but I was happy to learn it's an option.