"external nofollow" links for markdown? And in general, is it important for inbound links for my SEO?

Question

Search Engine Optimization

There is a self-written admin panel for bloggers. Articles there are added, removed, edited through markdown. And on the backend they are already converted to html. I like.
But, often for external links you need to add "external nofollow".
1) standard markdown doesn't allow you to do this? Should I write the extension myself?
2) External sites can be mine too, for such sites the absence of "external nofollow" is not a problem, they are mine anyway.
And then, when they are not mine, does the absence of "external nofollow" seriously undermine the SEO of my sites?

Answer 1

I have hundreds if not thousands of external links on my blog and this does not undermine my SEO in any way.