Hi Petr,
I did not get time to look at this, but I previously mapped the most important as shown in the figure below (It’s been some weeks since I did this but it should be correct). I am not familiar with PPM (particularly not with V6). Did you get it working with the current config in betaflight? I can’t see the resources. Also, PPM on this board may lead to timer collisions with the servo/motor assignments, so probably need new firmware build.
On the positive side, you may get away with the issue with the JST GPS connector on UART6 vs the inverted sbus pin which is also on serial 6, rendering the JST not usable if using sbus (not sure what the manufacturers rationale for this is). From the figure you can see that uart1 rx is available also from the LED pin.
