Discrepancy is big between new treadmill (Sole) and new Apple Watch. Did 2.3 miles in 40 minutes and Workout said .86 miles! I did calibrate watch. Will do it again but watch is not close. I don't walk 23 minutes/hour!

My guess is that the Sole F63 treadmill calculates your distance based on the number of revolutions of the tread. For a treadmill walk, the only way the watch can calculate the distance is by how (and how many times) you swing the arm your watch is on. And that is based on how you calibrated the watch on a previous 20 minute (at least) outdoor walk. If you hold onto a handrail on the treadmill during the workout, the watch distance might be considerably lower than what the treadmill calculates. Since (I assume) you calibrated your watch according to:

Calibrating your Apple Watch for improved Workout and Activity accuracy - Apple Support

you may also want to see:

Get the most accurate measurements using your Apple Watch - Apple Support