See the replies to this similar discussion and the links to more discussions therein: https://www.researchgate.net/post/Why_citation_score_for_author_publications_looks_different_on_Scopus_research_gate_google_scholar

Thanks, Wolfgang R. Dick , for the suggestions. The discussion does not provide the justification for the above-mentioned problem.

Citing Safaa Ismaeel's reply to the above mentioned discussion: "Citation scores differ across Scopus, ResearchGate, and Google Scholar due to variations in their databases, indexing criteria, coverage of journals, conference papers, books, and citation algorithms." I think this explains the reasons for the differences. It can hardly be said generally which of the platforms is the most reliable one. E.g., usually Google Scholar finds more citations of a given publication than ResearchGate, but sometimes it is vice versa. None of the platforms is complete with regard to publications and citations.

Thank you, Wolfgang R. Dick, for the reply. I think the differences in citation counts across these platforms are mainly due to the distinct databases they rely on. Scopus only tracks citations from publications that are indexed within the Scopus database. Similarly, Web of Science considers only those sources that are linked to its own indexing system. On the other hand, Google Scholar has a broader coverage since it includes both formally indexed sources and a wider range of materials such as conference papers, theses, preprints, and even institutional repositories. This is why citation counts on Google Scholar are typically higher and somewhat more comprehensive compared to Scopus and Web of Science, though the latter two are considered more selective and standardized.