Back in 2017, Google’s John Mueller said, according to SEO Roundtable, that all guest posts on blogs, no matter how often you contribute, should have all links set to “nofollow”. This past week he added, even if those links are not paid for – as long as those links can potential pass signals – they should also be nofollowed.
The part that's problematic is the links — if you're providing the content/the links, then those links shouldn't be passing signals & should have the rel-sponsored / rel-nofollow attached. It's fine to see it as a way of reaching a broader audience.
— 🐐 John 🐐 (@JohnMu) June 11, 2020
Google has previously said guest blogging is okay sometimes and not other times, adding some confusion to the situation and uncertainty for SEO’s managing campaigns for clients, and for website owners themselves.
It seems to us that, regardless of the frequency of your guest posts, and even if you don’t pay for writing it or don’t get paid for writing it, Google wants you to nofollow those links.
Having said that, there’s something that needs to be considered in parallel. Google uses “nofollow” as a suggestion, not a firm rule, so Google will – in most cases – still follow those links, and they’re likely to have some, albeit small, impact on SEO efforts (possibly something as simple as allowing Google to keep a count of the number of sites linking to you).