Google uses both schema.org markup and og:image meta tag for thumbnails in Google Search and Discover

Google clarified this within its Google image best practices and Google Discover documentation.

Google Clarifies How It Picks Thumbnails For Search, Discover

Google updated its Image SEO and Discover documentation to explain how schema markup and the og:image meta tag influence ...
Search Engine Roundtable

Google News Now Enables Image Selection For Publishers Via Schema Or og:image

Google has released their second version of the Google News Publisher Newsletter this week and there is one new thing with Google News for publishers. Publishers can now help Google News pick the ...