Same. Sometimes I've been asked by someone walking the queue to remove my boots. Never do, never a problem. I'm sure they just walk the queue so it feels like "something" is happening and you're not just waiting in yet another interminable queue.
if there are nails in the boots it triggers the metal detector. My boots aren’t glued (like timberlands and doc martins might be) and they trigger the detectors.
Almost all of my shoes nowadays have steel toes in them. I think my count for being told to not take them off because they expect them not to exceeds being asked to take them off. Never flown out of a non-EU country.
They do, just kind of “at random”. I had it sometimes a bit of everywhere in Europe.