So, this type of question comes up all the time, there’s a few things to consider
-What skills do you have? If you don’t have any relevant game development skills and experience then that makes it much more difficult to pretty much impossible.
-What resources do you have? RDR cost millions of dollars, took like 5 years and hundreds of people to make, do you have anything comparable?
-If you don’t have much to offer, then it’s difficult to get people to join the project, they will want to know that you are contributing as much as they are, and that you aren’t just the “idea guy”
-most projects where people are working for free fail, even ones that are much easier to make, if someone is not being paid to work on the project and the team is working remotely (everyone in different locations) then it’s really really difficult to keep people motivated and working.