Not sure about the EU-27, but the UK has rules about election ads, to the extent that Cambridge Analytica was a scandal. Some of that scandal was due to bribery and offering prostitutes, but even the aspects that were purely what is considered "normal" for targeting online advertising was unacceptable by UK political standards.
That said, part of the latter being scandalous assumes that they were actually capable of providing the service they claimed, which is something I find myself increasingly unable to believe due to how wildly badly I get categorised by the main advertising platforms — nationality, country of residence, language, gender, all wrong.
I don't know what various countries' norms are, but if people aren't used to political ads and are generally suspicious of the concept, an ad may have negative utility.
I know if I saw a paid ad for a candidate that would make me want to vote against them.
Paper flyers in your mailbox, and billboards in people's gardens, are some age-old and very common forms of advertisement during elections I've seen in multiple countries in Europe
In Spain we get nicely labeled "Political Propaganda" in the mail around election time. I think by law each party can send you one letter, and it has to have the "Political Propaganda" text on the outside.
It's pretty nice in that I can throw it all straight into the recycling bin!
There's a bunch of strictly regulated ad formats. Each party gets one "metal billboard" poster and I think one TV spot and that's it.
The most common form of political advertising by volume is probably unauthorized propaganda posters on public infrastructure, yeah. Those are annoying. Also stickers on traffic light poles and similar places.
Australia small signs (100cmx50cm size) are common. Billboards you’d see down a commercial street are probably private property and often are political also.
