I find it hard to see which GPIOs are free to use on ESP32 models (including development boards and variants). The pinout diagrams are not enough in my opinion. Is it just me or could the documentation be improved there?
I think there may be a bit of a communication mismatch. Pinout diagrams literally describe the pins that are brought out of a module / board for you to use. Maybe you can provide a link to a diagram that you are referring to and explain what information you are missing? A pinout diagram for me is something
like this and the table above it...
If you want more specific information concerning specific pin capabilities, there are always the datasheets of the module and one level lower, the processor to peruse. I.e.
this document for the ESP32,
here's an overview over all products' datasheets.