When I try to run Simple Filters the window shows only help&development system reported error that Simple Filters widget has no representation. Could I ask for help?
It is probably because your username contain a special (non-ASCII) character. See more details here: SimpleITK is not available on Windows if Slicer is installed in a path that contains special characters · Issue #5383 · Slicer/Slicer · GitHub
For now, I would recommend to reinstall Slicer at the step you need to choose the install location choose a path that does not contain any special characters.
I didn’t create an account yet. At least no data in User settings is applied
Does your OS (eg Windows, macOS, etc) username include the special character “ł” as in your name “Michał”?
I just changed it to “l” but default folder still has “ł”
Changing the username will probably not change the already created profile path (because doing so could break already installed software). I would expect that other software will have problems with your profile folder containing special characters, so it could make sense to create a new user with a simple username. If the goal is to make Slicer work with minimum effort, you can install it in a different location (for example, c:\Slicer).