I have never been aware of that usage. It seems to be non-standard as none of the dictionaries here mentions that meaning.
Interested in Language
As far as I know, Showstopper means a part of something longer is so impressive that the whole show is stopped to appreciate that part.
But, I have seen usage of Showstopper (even with native speakers) as something without which a project (let's say) cannot go forward. It stops, but not to appreciate the impressiveness, but because it is absolutely necessary to have.
Any comment, please?
A 'deal breaker' is a term that is often used to describe a situation that has reached an impasse.
What is the specific context for your sentence?
Yes, it can be used in that way. It is something that literally puts a stop to the show, meaning the project.
let's say, A research project is going on to develop a product. It needs input from all departments viz. Marketing, Design
, Production, Operation etc. Now, while the project is going on, Finance department is always late with their input. The project manager says "As, this is only a research project and a budget has been allocated, finance input is not a showstopper, though it is good to have."