Thanks, Kent @theluthier and Vadim @harbinger_ua, for your answers😀! I’ve (before reading your posts) used “fSpy” which calculated appromimately 40mm focal length and after importing the generated output file into Blender resulted in a focal length of approximately 33 mm (I don’t know why it’s imported like this):
1) fSpy: The mill tower’s entry door is set to a height of 2 meters (in order to make “fSpy” calculate the camera’s distance)

2) Imported into Blender:

My “Fantasy House” modeled with 50 mm focal length resulting in a too long Y axis extension:

This dummy guy is 2 meters tall with hat.