Whereas a research proposal is a statement of intent, related to answering a research question, a grant application is a specific request for funding to complete the research proposed. Of course, there are elements of overlap between the two documents; it's the purpose of the document that defines one or the other.
you can read more here: https://scientific-publishing.webshop.elsevier.com/research-process/writing-scientific-research-project-proposal/#:~:text=Whereas%20a%20research%20proposal%20is,defines%20one%20or%20the%20other.
and this source as well : https://www.linkedin.com/pulse/whats-difference-between-research-proposal-protocol-hedrick-ma