Right now, Related Posts links all include a nofollow rel parameter. A while back, we added a filter, jetpack_relatedposts_filter_post_link_rel, allowing you to remove that parameter if you'd rather have these links followed by search engine bots by default (see #2299).

@xyu Should we consider removing the nofollow parameter by default, since Google seems to be okay with that?
https://www.seroundtable.com/related-post-blog-links-google-nofollow-21546.html

Reported here:
https://wordpress.org/support/topic/change-jetpack-related-posts-nofollow-to-dofollow?replies=5&view=all