Ah, got it. When you calibrate the machine, the maslow.yaml file gets restructured and several things get filled in and moved around. I believe the “probe:” entry is added in automatically by FluidNC during that process. So, try calibrating first then download the calibrated maslow.yaml file and open that file in a text editor like Notepad. Hopefully, it should be in there now.
Also, if you have a recent backup of your yaml file that is post-calibration, you can likely find the setting there and use the backup. I don’t think much often changes on the yaml side of things and using an older one is usually ok.