The critical difference for me is if they ask while you're eating, perhaps 5 minutes after serving your table, that's OK it means they are genuinely interested in improving your experience and it's an opportunity to correct minor problems.

If they ask after you've eaten, that would be rude, from my British perspective.

The after-meal ask is to see if 1) you want dessert or 2) you want your soft drink refilled or to purchase an additional alcoholic beverage. Honestly, I think the "waiters keep pestering me" perception from Europeans is heavily influenced by the refill checks, which by-and-large aren't a thing in Europe.