Hi there!
Where I can publish my posts for cybersec?
Something like for developers dev.to, but more for security
Create your own blog.
LinkedIn
I concur with emb02 - create your own blog.
Personally, I prefer my to host my own blog over Medium/Substack/other large "article hosting" sites because I have clear understanding over how my content is used. In recent years I have grown pretty wary of content platforms and how they may monetise or otherwise use your content.
I'm not about to pretend I am the next Bruce Schneier or Brian Krebs, and I can probably count the number of visitors to my site in a month on my hands, but I am happy in being able to write the content I want and put it somewhere I can trust.
Creating your own block is the best way to go. Blogger, Medium etc are all good platforms for that.