The New Tab Page is apparently reserved for Microsoft Content. If the computer is domain joined it may be changeable using policy but otherwise you'd have to switch to Chrome or Chromium.
The new tab page at least needs a "Blank" option that is truly blank and a URL option. It's frustrating because Edge is so close to being adequate.
This along with nonsense like Weather, MS Rewards, Permanent Search Box and Office 365 links burned into the New Tab Page, and strange default integrations like "Show suggestions from Pinterest in your collections" and "Save time and money with Shopping in Microsoft Edge" and un-interruptible modal fullscreen intro animations (first launch, update etc) are signs that Microsoft is only interested in monetizing Chrome rather than building a great default browser.
If they were smart they would make it simple to turn off all the non-sense sales, ads and forced MS content and tracking. Tech folks won't mind that it's there for 99% of the population as long as we can turn it off. If they keep piling on the crap tech people will just disable/remove and install an alternate as default for themselves and everyone they know and every computer they work on. It's happened before.
Throw us a bone here MS, most people won't change the default, but let those of us who need to do so without installing a 3rd party browser.
Folks are fake joining domains to work around this (not recommended)
https://hitco.at/blog/apply-edge-policies-for-non-domain-joined-devices/
There is demand for it.
