Eventually found the answer in this list. I'd have guessed it, but some cruel programmer decided to make it the only canonical name with capitalisation, and apparently the names are case sensitive.
It's now: ms-settings:easeofaccess-MousePointer
This browser is no longer supported.
Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support.
We use a GPO to show only particular settings items to students. This requires the canonical name of particular settings pages.
It seems like the canonical name has changed for Ease of Access -> Mouse pointer (20H2, but I believe this stopped working with 20H1). This Page was previously called Cursor and Pointer in 1909, and it's previous canonical name (listed here) as easeofaccess-cursorandpointersize no longer works.
For example, opening run and typing ms-settings:easeofaccess-cursorandpointersize on a Windows 1909 machine correctly opens Cursor and Pointer. Doing the same on 20H2 only opens the settings home page - it couldn't find a page with that name.
I have no idea where to find, or how to figure out the new value, and so far everything I've tried (including wild guessing) has failed. I'd appreciate any and all help with this, including how to find canonical names that don't seem to have been published..