1. The adjustment only works in anything but x1 mode.

2. The adjustment corrects the squareness of a square wave. It makes the divider resistive.

3. Probes are designed for a certain input Z e.g. 1 M 22 || pf and freq response
Make sure the scope isn't 50 ohms.

4. For the adj, the scope should be DC coupled.

5. Scope could be in UNCAL mode. Freq or voltage.

6. Check voltage with a DC source. Freq: Try the AC line for frequency.