Gutenberg is developed separately https://github.com/WordPress/gutenberg and the latest version currently is
How to find out which version of Gutenberg is included in my WordPress installation?
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You can find the versions in WordPress here with this recently created document: https://developer.wordpress.org/block-editor/principles/versions-in-wordpress/ You weren't alone in wanting to have this information :) As mentioned above, it can be tricky to directly line up versions but this is the closest approximation currently. When WordPress 5.5 is launched, this document will be updated.
I don't know if there's a way to figure this out for every version; but for 5.3, I eventually found this official blog post after extensive searching. (WordPress 5.3 has Gutenberg 6.3 by default)