The most challenging maps for you.

Chingis, after your explanation, the situation became clearer. If you started your acquaintance with the "Heroes" series with the 6th installment, then it's understandable.
"Heroes 3" and "Heroes 6" are very different games! Personally, after reading reviews about the 6th installment, I didn't want to spend money on a new video card and extra memory to play this "masterpiece": in my opinion, only the horns and hooves of a strategy remained. :( Well, this was already discussed in detail before the release of "Heroes 6".
Perhaps I expressed myself too harshly, but believe me: it's worth learning to play "Heroes 3" well - and you won't want to play other versions anymore! I, for example, rarely want to play other games. :)
By the way, did you know that in the single-player game in "Heroes 3," the timer is not used by default, and the player's turn time is not limited!
Yes, and I also wanted to note one feature of the auto-battle (I read about this somewhere a long time ago): most often, its results are better than in a "manual" battle for a human player. Moreover: they wrote that it is not possible to achieve such results even for the strongest players; usually, the losses are noticeably greater. The conclusion was that the calculation algorithm in the auto-battle is imperfect and does not take into account all the nuances - hence the difference. Therefore, the auto-battle (if we don't count "clearing" small neutrals to save time) can, in a sense, be almost equated to cheating. But I think that with experience, you will always prefer to fight enemies yourself. And win! Good luck to you on the battlefields!