Sure you need an XC frame? New gravels become more XC nowadays. Check SPCycle G028/Mondince FM366 (57 mm clearance) or Mondince FM356 (61 mm) in the neighboring forum branch. Can't comment on anything special about them, just the first frames popped up in there. Perhaps there're some other options.
Also, there was a thread here somewhere about a beach racing bike, don't remember the frame.
Thank you very much for the information about the brand-new gravel frames!
I wasn’t aware that the tire clearance was already up to 700x61. That really makes things easier.
And it’s also become clear to me that a modern MTB frame was designed for straight handlebars.
Drop bars, on the other hand, typically move the brake levers 80–120 mm further forward (depending on the handlebars and hoods).
So if you simply fit a drop bar to an MTB frame, the cockpit often ends up being too long.
This means you’d have to choose either a long frame with a short stem (50 mm) or a short frame with a slightly longer stem.
In any case, I’m looking at dedicated gravel frames, which have the stack and reach specific to drop bars and, most importantly, offer significantly more tire clearance.