Haven't heard anything about this. If you are traveling to Upper Mustang or Manaslu you need a guide but for other places, its not required.

Where can I find this info in a government website ?

From Namche Bazar yes , because alot of solo hikers went missing this past year

They are trying to implement this rule since few trekkers are missing.  It's either a guide or a porter they say, but have not implemented this yet.

Can anyone confirm that a guide is required (due to some recently enacted policy) to hike the Everest base camp?

I came across this on TripAdvisor which references a few Facebook posts but I don’t use Facebook and I don’t see any info online or on the Nepal immigration website.

Mandatory Guide for trekking above 3000m