It means: Too many cooks spoil the broth. just expressed with larger words.
Too many cooks spoil the broth.
You would use "a plethora" before the noun, as in "a plethora of options."
Plethora is singular and the plural form is plethoras
(Plethora means an abundant excess as a bountiful excesss such as riches.)"The Thanksgiving feast was a plethora of favorite foods of the family.""There was a plethora of costumes to choose from for the masquerade.""From the plethora of possible names for the project, he chose the most apt."
There was a plethora of food on the table at Thanksgiving.
Plethora is a noun.
"Is", since plethora is in singular form
The noun plethora (a plethora) uses singular verb forms.The word plethora is an uncountable (mass) noun, a type of aggregate noun that refers to an unspecified but large number of elements, e.g. a plethora of choices.
Plethora is singular and the plural form is plethoras.
The plethora of escapes from supposedly secure prisons embarrassed the hapless wardens. The success of his videos inspired a plethora of imitators.
"There was a plethora of items in her desk." "Plethora" is not a verb / action word, so it will not change forms from a present to a past tense.
superabundance, an excess