Confusion about solar cells and MPPT
A DC-DC converter under MPPT control must have a suitable load on it in which to dump all the power the panels can supply, for instance charging a big enough battery bank, or an inverter into the area's mains power supply.

It then simply increases the current it draws from the panels, which drops the panel voltage, until the algorithm decides that it is drawing the maximum power it can. Drawing any more current at this point would reduce the voltage so much that the power drops.

The MPPT controller doesn't have magic in it to predict what the voltage will drop will be. It will dither the current either side of the operating point, and see what the conditions are, and work near the MPPT. That way it can keep up with changing illumination conditions.