The difference between Agender and Gender-neutral

When used as adjectives, agender means without an associated gender, whereas gender-neutral means applicable or available to all genders.

check bellow for the other definitions of Agender and Gender-neutral

Agender as an adjective (rare):

Without an associated gender.

Examples:

"An agender noun includes both the masculine and feminine forms."

Gender-neutral as an adjective:

Applicable or available to all genders.

Examples:

"The women's sleeping quarters are on the left side of the dormitory, the men's are on the right; gender-neutral restrooms are located in the middle."

"Many modern laws use gender-neutral constructions like "he or she" in place of the old, supposedly unmarked "he"."
Gender-neutral as an adjective:

Not indicating or restricted by gender, and thus applicable or available to those of any gender and to those of no gender.

Examples:

"Gender-neutral pronouns like "ey" and "ze" are used by many genderqueer, intersex, and neutrois individuals."
Gender-neutral as an adjective (grammar):

In languages where words are assigned to one gender or another, lacking such an assignment.