I unpack the contents of the 001_NCF - Special Edition folder into a clean copy of the game, version 3.1, run H5_Game.NCF, and start the NCF - Special Edition_2021-02-21 map. During loading, the game crashes. (This happens with any other maps as well). What should I do?
There is no such problem with 002_3rd_Level_Upgrade.

Your computer is not powerful enough (the map has many creatures and buildings). Reduce the graphics settings to the minimum; this should help. In the game itself, you can then set the quality to "normal" and the resolution to, for example, 1360x768.

Another solution in your situation is to use the map editor (H5_MapEditor.NCF.exe) to remove some of the creatures from the NCF - Special Edition_2021-02-23.h5m map (for example, 1/4, 1/3, or 1/2) - this map will no longer crash when loading. The crash occurs precisely because the map is saturated with objects. The NCF - Level_Upgrade_2021-01-17.h5m map does not crash when loading because it actually has no objects (creatures).
This has been personally tested on a computer and a laptop. With a powerful computer, there are no problems; on the laptop, this map 100% runs at a resolution of 640x480 and quality "very low". After the map starts, I recommend setting the resolution to 1360x768 and the quality to "normal", and then you can play.