There is a convoluted non-extension method.
-
Registry change. See here: https://learn.microsoft.com/en-us/DeployEdge/microsoft-edge-policies/newtabpagelocation
-
That will be all you need if you're enrolled in a domain or mobile device management. If you're not you can fake being in a MDM environment via another registry change. See here for that: https://hitco.at/blog/apply-edge-policies-for-non-domain-joined-devices/
Honestly user hostile behavior by MS here, but as with most things can be defeated one way or another if you're able to waste time on it.