How to manually insert related posts anywhere in the posts?

I am new to WordPress. I want a widget/plugin for inserting related posts anywhere I want in my post content. I already have tried so many plugins and unfortunately I failed to find something I want.

I tried Inline Related Posts plugin, but it just automatically add related posts. I want it to be manual.

An example of what I want to do: Imagine I have long post. I want to add a related post after third paragraph, another related post a few paragraph later, yet another related post after that and so on.

Also I want something to work in the classic editor.

Something simple is fine. I just want it to display something like "Read more: [the link of related post]".

Thanks for reading and for any help.