It seems like it recognizes it, but the this happens after clicking .p8 file:

//edit: Also it seems that upper-case charset contains few cool c64-like semi-graphics. Can we access this in next version with shift?

This might be related to issues I've had trying to use the -run option: https://www.lexaloffle.com/bbs/?tid=2553

So it might be the case that it's set up correctly, we just need -run to work. :)

no, this was without -run. It just can't load, hence -run doesn't work (as you first need to load cart in order to run it).