What is the plural form of "scenery"?
The noun 'scenery' is an uncountable (mass) noun, it has NO plural form.
The noun 'scenery' is a type of uncountable noun called an aggregate noun, a word representing an indefinite number of elements.
A partitive noun (also called a noun counter) is a noun used to count or quantify an uncountable noun; for example:
a view of scenery
a lot of scenery
a background of scenery
The noun 'scenery' is also used on its own; for example:
We enjoyed the scenery on the drive.
It's a depressed neighborhood with a lot of sad scenery.
We spent the afternoon painting the scenery.