"a company of biscuit manufacturers" means "a company has biscuit

does “a company of biscuit manufacturers” mean “a company has biscuit manufacturers”?

No, it means that the company manufactures biscuits.

what is the difference between ‘a company of biscuit manufacturers’ and ‘a company of biscuit manufacturer’

“a company of biscuit manufacturer” is not correct English.

thanks a lot

i find another problem.
in this saying “a car/computer manufacturer”,why use the world “manufacturer” rather than “manufacturers”

“a car/computer manufacturers” is wrong because the article “a” is incompatible with the plural “manufacturers”.

In “a company of biscuit manufacturers”, on the other hand, the article “a” applies to “company”, not “manufacturers”.

Simplest to say: A biscuit manufacturing company.