See the "Sharing and hosting policy FAQs" by Elsevier, particularly for ResearchGate: https://www.elsevier.com/about/policies-and-standards/sharing/policy-faq#3-researchgate. For other publishers, see ResearchGate's link list at https://help.researchgate.net/hc/en-us/articles/14295462972433-Directory-of-Publisher-Copyright-Policies. - When the upload of published versions is not allowed, I produce "preprint" versions after publication to be able to upload full-texts to ResearchGate (provided that preprints are allowed by the publisher).

Thanks Wolfgang!