The aspect ratio is displayed incorrectly.

Then another question, in which files are the campaign saves and campaign progress stored? I need to transfer them in such a way that the old monitor settings are not transferred, and the game will then set them according to the new monitor, as happened in the original game, where the saves were not important.

Settings and saves in the original game and expansions are stored in different paths. For example, for Tribes of the East, it's \User Documents\My Games\Heroes of Might and Magic V — Tribes of the East\saves. The settings file is also there: user.cfg for the original game, and user_a1, user_a2 for the expansions. But there's no point in these manipulations; the proportions in widescreen mode will be distorted everywhere except for Tribes of the East with patch 3.1. No matter how you tweak the settings, it's all inside the executable file. There is an option to play the old campaigns under Tribes of the East 3.1, but you'll have to download a mod to unlock the previous campaigns and play without distortions.