Maybe not possible in the specific country you're thinking about, with their specific implementation of "freedom of speech", but it's hardly the only one, and not all of them are incompatible with outlawing lobbying (if the US one even is, I dunno).

If you try to ban lobbying you will incidentally criminalize basically all political speech. White papers are a form of lobbying, providing testimony is a form of lobbying, running an ad campaign is lobbying, speaking with your congressional representative is lobbying.

It'd simply have to be carefully drafted policy rather than an internet comment.

So simple it's indescribable

This notion always puzzles me. It's not a complex idea.

Just like, say, banning GMO bananas. But such regulation is a whole text which may need to define or refer to definitions of "GMO" and "banana", specify what's banned, exemptions, enforcement authority, penalties, and so on. Maybe 10 pages of legalese. It requires time, expertise, research. But it's still just a ban on GMO bananas.

Or a programmed UI button to show a message. Simple. The specifics of the execution are a separate matter.

It's not "indescribable", but no one will describe it to you ad hoc and expecting it is silly.

What's "it"? Speaking in public?

Making strawmen. Your position of "policy is impossible to write" is inane.