Requests for full texts are only possible when there is no full text for download. It is not so that ResearchGate "hides" these - they are just missing. You have to upload the full text, or send it privately, or decline (or ignore) the request. See https://help.researchgate.net/hc/en-us/articles/14292986311825-Discovering-and-requesting-research for more explanations. See also my reply to https://www.researchgate.net/post/Requests_for_Documents.