Can anyone with more legal/political nous than I, perhaps, explain what they think the point of this may be..?

If there is any, most likely winning popularity with the Branch Covidians, who say: wow, our wonderful government is trying to make sure that people don't travel and sheeit. And if someone does travel, they will be able to point back to this to prove that: "see, we did everything we could to warn people and make sure they would be aware of the fact that this is NOT allowed!"

Furthermore, this sort of threat increases the presence - and thereby the power - of the government in people's lives.

It may also just be that there is a budget for 'information' and they had to spend it on something.

Of course, this is just speculation.

It's like... Stereotypical "evil government" shit...

First time?

What exactly does this ad even achieve, lol..?

They're not necessarily thinking about what it achieves. That's quite common for governments.