Please note that ResearchGate is not a publisher or journal, you cannot "publish" a paper here. It is a platform for papers published in journals, or to present unpublished texts, data etc. See also "Is ResearchGate a publisher?" in https://help.researchgate.net/hc/en-us/articles/14292596164753. See this help page ("How to add research") for instructions how to add published or unpublished research to ResearchGate: https://help.researchgate.net/hc/en-us/articles/14293005132305
As Dr. Wolfgang R. Dick replied, like Academia ResearchGate is a SM platform where scholars can exchange their published or unpublished research text, data, ideas etc.