I think you'd want with a bike that's pretty classic to start with. That will mean a bike that won't feel dated in a few short years.
Steel and mechanical shifters. Done correctly, even with disc brakes, you'll be at 18lbs including cages and pedals and it's not going to be much different in 20 years.
I would get a Ritte Satyr with mechanical Ultegra a hydraulic discs. The Mavic Open Pro rims on the best hubs you can afford. Finish it off with carbon and titanium bits. It'd be a sweet bike forever. And you'd have an endurance and gravel capable bike from the influence of a great American frame builder.
I have a three older steel road bikes. I can hang with everyone but the mid 20s racers. I don't think the finest modern road bike on the planet would help me catch those guys. I get compliments on every ride and I still pass a lot more than I get passed.
Think about it.