As someone who’s been a bit down the sizing/bike-fit rabbit hole lately, I must say I keep coming back to Dave Moulton’s now quite old advice: if your limbs are broadly proportionate in length to your height, go with 2/3 of your inseam, and see if the manufacturer’s height/size recommendations align with that. If it does, that’s your frame size. If it doesn’t, it’s trickier, especially if you have long legs and a short body, but remember it’s generally easier to make a bike fit bigger than it is smaller.
For CX, though, I’d be inclined to size up to minimise toe overlap and for easier shouldering.