I've been biking for over three decades and always tend to do the 'standard sideways nod of the head' in the UK or the 'two-finger downward wave' in Europe.

The one thing that stands out is the difference in the reactions of other bikers in the UK depending on the type of bike I'm on at the time - given I'm lucky with three different styles/makes of bike at the moment, it's a real mix of reactions.

For example - UK bikers tend not to 'nod' back if I'm on my old Harley (1996 Softail) - in fact, even other UK Harley riders tend not to return the 'nod'. On my KTM (2022 890 adventure) - there is more of a mixed reaction here, basically a better response from other bikers, but again, not great, but an improvement over the Harley. Finally, BMW (2011 K1600GT), is the best response in the UK while on this; while it is still not 100% it is still better than the other two bikes.

The interesting thing here is foreign riders don't seem to mind what bike I'm on, but here in the UK, there is a definite change in attitude; I am just wondering what others have seen regarding this.

That's because we're a fickle lot over here, too hung up on the image what we think we are projecting.
I'll wave or nod at anyone on two wheels and usually get a response if I'm on the bike. Much less so if I'm on the scooter, and if they do you can see the horror once the realise what they've done 😱
But that's nothing to response if I pass a bike on the scooter 🙂

I'm happy to nod or wave at anybody on 2 wheels no matter what they are on, Unless there wearing a black hoody and a balaclava then I'm more likely to kick then into the back of a dustcart as they pass                                                                                                                                                                             

i herd that about jp i only nod to the thing only i can see and bikers on bike not in cars just bikes                                                                                                                                                                             

When I was out and about on Christmas Eve I passed loads of bikes, nodding to each and every one but barely 25% responded... So sad 😔                                                                                                                                                                             

I nodded today and got a nod and a wink in return, it was a bloke mind, so, I'm a little confused about that, still, a nod and a wink, I'll take it, caught it on the gopro too, little hard to see the wink mind :)

https://1drv.ms/v/s!AhYlGmUcEi2SkbUBTo0OjgeRjryCyw?e=uiilqb
(Quality is terrible if you stream this, even at 1080p, download (top left) would better)

I'll nod at everyone on two or even three wheels, forget myself sometimes when I'm in my car & do it.
I have to agree with Bat66 though, get a better response on the continent than in Britain.