Thanks for the great suggestions! The website 99spokes was especially useful to compare bikes. I have found, however, that there is a great variation in the standover height the manufacturer claims and what it actually is when you throw a leg over the bike, so it seems that manufacturers measure the SO at different spots along the sloping top tube.
I've tried out a Specialized Diverge, Norco Search, Kona Rove, Salsa Journeyman, Cannondale Topstone, and a Trek Checkpoint. The main issue is that while shops usually have a 52 or 54 in stock, it's less common to have anything smaller especially in the mid-level range. I'm pretty reluctant to buy a bike sight unseen so I'm somewhat limited to the "usual" brands found in my area. At least I've determined that I need to have hydraulic brakes because of my short fingers, (affordable) steel is too heavy, and that a 1x drivetrain probably won't be the ideal option for winter riding.
Second follow up question: The Norco Search comes with 650b wheels in the 48 and 700 wheels in the 50.5. The 48 would be a special order but I tried the 50.5 and have sufficient standover and it felt good riding, though it felt better when they put a slightly shorter stem on it. Any thoughts on how a smaller bike with 650b wheels would ride differently from a larger bike with 700 wheels? I'm a weak hill climber, and I'm not really comfortable above 100 rpm for any length of time (I tend to push heavier gears at a lower cadence), and on bikes with a 700 wheel I seem to prefer a crank arm length of 165 (170 feels like too big a circle for my legs), if that makes any difference.
Third follow up question: on something like the Checkpoint, is it possible to have one 700 wheelset (for the road) and a 650b wheelset (for gravel) or do other things have to change when you change wheel sizes so it wouldn't be practical?