It's because the AF micro adjustments are only for A mount lenses with the adapter."Allows you to adjust the auto-focusing position and register an adjusted value for each lens when using A-mount lenses with an LA-EA2 or LA-EA4 Mount Adaptor (sold separately).Use this function only when adjustments are needed. Note that the auto focus function may not be performed at a proper position when using this adjustment."https://helpguide.sony.net/ilc/1930/v1/en/contents/TP0002688363.html?search=micro%20adjustment
Thanks! another post explained that the autofocus is on the sensor so micro adjustment is not necessary on a mirrorless camera