let's say someone doesn't want to install additional upgrades/programs/DLLs, etc., and how can this be checked? - a program is needed to check exactly what the opponent has in the Heroes folder (impossible) or in the running Heroes game (like checking an IP address on the internet, it immediately shows what else you are using).

I see it this way. A database is created containing the MD5 hashes (a 128-bit identifier for a data block) for all "bad" programs and libraries related to Heroes (and not just in the Heroes folder, but everywhere). And, let's say, during the connection with an opponent, the data is compared, and, accordingly, if "bad" programs are running, the ability to play is prohibited. And also, notify (if possible, block the Heroes game) if such a program was launched after the game started. Text files are more complicated. And, in fact, who will do this.