I’d normally recommend what I use (a 531 retro tourer with Shimano 3x, 32c, flat bars) but you specced flat bars and discs. A few hundred quid or less, not thousands. It goes better on road and paths than any modern (or other) bike I’ve ridden. Silent, swift, strong and magically comfortable. It even carries 20 kilos of groceries on an evening (and brakes with 100kg of me plus said groceries on my hilly streets)
I’d say get similar, then buy nice gear, lights, a holiday etc with what’s left over. But discs it doesn’t have!
So I’m going to say Giant ToughRoad SLR 1 Flat Bar Gravel Bike (2021 Grey). Job done.
(Just had a butchers online seem to be in stock at Pauls Cycles for £1299, similar prices elsewhere).
Also recommend spending some money on good proper road-spec lights (with cutoff beam and decent spread/throw) or even oush for dynamo hub + lights included in a package deal to max out your budget?