Solar panels/blankets. Potential difference

It is best if they are the same voltage for maximum efficiency.

If its a PWM controller and the batteries a low then basically it is a switch that is turned on so solar panel voltage will be similar to the battery voltage so any panel voltage difference doesn't really matter

If it is a MPPT charger then there will be some inefficiencies as the charger will seek the MPV and if it is aove the voltage of the lower voltage panel then that panel is going to supply any real power. A good MPPT should look for mutiple MPV points, the its not so bad, a cheaper unit may not.

A lot of the answers you will get are theoretical so in essence just guesses.
If you already have the panels I would suggest setting them up in a test environment then with a clamp meter look at where and how much current is flowing.

From the iTechworld website CAN I MIX DIFFERENT SIZE SOLAR PANELS?

Hi Lyndon,
Have a read of this link - it is much better than the iTechworld one as they have totally ignored voltage levels, which is kinda important...
https://mowgli-adventures.com/wiring-solar-panels-in-series-vs-parallel/?utm_source=WebStory&fbclid=IwAR24er6rYSIAxyIYzRh2AeMGpbKEA89r2e-jJpF_UHDAN4gklIdcE6CSejY#calc

Hope this helps
Bryan