TYPO3 Core

From the documentation:
"In TYPO3 versions below 10.4, the doktype was restricted to numbers smaller than 200 if the custom page type should be displayed in the frontend, and larger than 200 when it is just some storage. This limitation no longer exists, so you can choose a number at will."
https://docs.typo3.org/m/typo3/reference-coreapi/10.4/en-us/ApiOverview/PageTypes/Index.html?highlight=page%20types

But:
When adding a custom doktype >= (int)200 the user can't set links to these pages via the link browser.

In typo3/sysext/backend/Classes/Tree/View/ElementBrowserPageTreeView.php
the function ext_isLinkable returns false if the doktype is > PageRepository::DOKTYPE_SPACER (199)

public function ext_isLinkable($doktype, $uid)
{
    return $uid && $doktype < PageRepository::DOKTYPE_SPACER;
}

The method is absolutly the same on current main (so v11 also).