Nofollow – on a post basis?

to be fair I don’t understand why this isn’t a core function of wordpress

There’s no proper API for this in Gutenberg. All other implementations, like the one from Yoast SEO, are hacked into the editor and may break the entire editing experience in any future Gutenberg update. They have enough developers and an accompanying release schedule to play catchup, something I cannot afford.

There’s a discussion about this here, with a lot of pushback and misunderstanding from the team behind Gutenberg: https://github.com/WordPress/gutenberg/issues/23011.

It was actually planned to be included in Gutenberg (see https://github.com/WordPress/gutenberg/pull/16609), but it was blocked because another issue would cover it but didn’t… eh… yea.

We have an open/active feature request for it here: https://github.com/sybrew/the-seo-framework/issues/568.

In the meantime, you can add this feature via a plugin like this one: https://www.ads-software.com/plugins/block-options/.

Dear @cybr
Many thanks for the clarification and suggestion.
Piet