What is best way to fight with flickering shadows?
Stencil shadows is by default bad.
PSSM really likes to flicked and to displace - atleast for me.
Im seen videos where peoples show really(or normal) good quality shadows in this engine.
I really hope here is some experienced persons who know best ways or shadow shaders to use.

stencil shadows are not bad, but have limitations, and sometimes slow. for free/extra users it is the only relatively nice solution, beside decal shadows and static lightmaps.

pssm shadows is not compatible at the moment with self shadows on entitites having alpha skin. but it is on the roadmap to be solved, hopefully soon. this cause currently flickering.

another bug said to be fixed in current beta, is when you use pssm self shadows on entities having normal maps. currently it results in black shadows or engine crash depending on the actual shader. (I reported it)

so if something does not work report it on bugs sectiona, and will be fixed. I do it and works. but sometimes I'm wrong and do something wrong, and not a bug...

if you cannot set PSSM shadows alone fine, try my editor, there are real time adjustment possibilities, to set bias and other parameters well (there is also a minor bug that disturbes bias settings, but I reported it, and fixed in next update). you can load yuur wmb level, but a terrain must be contained.

Thanks for answer. Seems all of your said helps to make my problems. And extra annoying flickering comes from parallel planes to sun.

I wish there could be more light source shadows which works really nice.

yes, flat planes are a problem. try stencil_blur(1.2); that blurs pssm shadows too, usually looks fine. and you can increase the smoothing factors in the vp_pssm.fx. I use currently 7 for the near value instead of 5 for the 1st split, I left the far value 3 for the last 2 splits, and introduced a mid value 5 for the 2nd split.