> Where I live, it's customary to let other drivers know by flashing your brights when they're blinding you

I do this here in the UK too, it happens a fair amount in the countryside where people will forget to turn off their high-beams as they reach a junction, and some of them driving older vehicles that won't detect oncoming traffic and auto-dip.

Like you, I increasingly have the issue, in the city, that some lights are so damn bright I literally can't tell if they're using high-beams other than the fact I've grown to know which models are the worst for it. Flashing them is pointless because they won't understand unless someone actually stops to tell them one day.

Legislation needs to fix this, they never should have been allowed to be sold like this, and I hope mandates for changes to the annual inspections (MOT here in UK) come in to correct it for existing vehicles.