Severe lag in the game.

It used to be. Please share the game build and which expansions you have! For example, "Alexander" puts much less load on the processor.
On XP, you can check the box for "Use software rendering," and then the game will use a "16:9" resolution, but the image quality will suffer.

I have: Heroes 4, patched to 2.0 (before the patch, there were very strong slowdowns, but not from the beginning of the game, but after some time (the memory was completely loaded, and no cleaning helped - only restarting the game)); Armageddon's Blade (2.2); The Shadow of Death (3.0). All from Buka, installed around 2006. I usually use the version in which the map was created. I installed the pirated "Alexander," but I haven't used it. The fourth installment put a moderate load on the processor, but the memory overload was initially a problem with the fourth installment. By the way, regarding "Alexander" - this has been written about repeatedly, and I confirm - unlike Buka's build, the collection contains maps with bugs, unverified, and unplayable maps, including campaigns that may simply be compiled from different maps that have no logical connection.
Regarding software rendering in XP - I searched the internet, but I didn't find anything useful about where to find it and how to enable it to test it:smile35:. As I understand it, it is more needed for online (internet) play.
I will try the CPU-Control utility, but not for the game - my single-core Sempron-1600 could handle the game until the motherboard failed.