When I used to do Europe regularly all the brit drivers would give a little wave, specially near Calais and along the corridor. Last time I went over I didn’t see many brits, the few I did see didn’t wave.
I now do a bit for the someone involved in the events industry and it seems that all tour trucks flash/wave.
Most car transporter drivers wave at each other.
When coming out of some of the stores service yards if there’s say a milk wagon waiting or another delivery from a different depot I always give a cheery wave. What really annoys me though is the impatient rigid bread drivers who can’t wait for you to get out the way and blank you even though you give them a wave.
I do find when trawling along a quiet road at night/early morning if another driver (from a different company) gives you a cheery flash/wave it kind if makes you focus a bit better, breaks up the mundane stretch of black tarmac. Unless you get a sudden flash which you weren’t expecting and you think $#*t what’s up lol.
I find I get more flashes off drivers from different companies/depots than I do from wagons from my own depot.