So I bought Heroes 4 Complete from GOG and the tooltip that normally appears when you hover your mouse over an object flickers, making it unreradable.

I used to own a boxed copy of Heroes 4 and there was no such problem. This is really annoying because the tooltip would show you how much damage an attack would actually do in combat. How do I fix this?

Lots of graphical glitches that I had with HoMM4 were solved when I used dxwnd.
https://www.gog.com/forum/heroes_of_might_and_magic_series/heroes_of_might_and_magic_4_homm_iv_slow_animations_on_1280x1024/post31

Maybe it will help you too?

Thanks a lot for the help, yesterday I tried the settings for dxwnd I've found in that thread, and also tried different combinations and it still has this weird graphic glitch. I had this exact same problem on a totally different pc too, it only worked normally again when I reinstalled the OS. Maybe some software is causing this problem, I don't know. I tried booting up my windows with everything disabled on startup to see what's interfering but still no luck. The game works fine on my laptop though. My PC and laptop both running Windows 7 64bit my old pc had this as well.
I'd really like to play this on my pc and I can't do it whithout those damn tooltips.
I really appreciate your help though.

Hello future people. I have found a temporary workaround for this problem. When you hold down the Alt button, the tooltips will appear. However they will disappear again, when you let go of the Alt button.

This will likely be annoying but still better than no solution. Because I've tried DXWND and the Heroes 4 GL wrapper and still get flickering tooltips. Running Windows 7 64-bit with an Nvidia GTX1070 graphics card.

for anyone having this problem,

[task manager -> details] tab causes this problem. if you open the task manager to set affinity and leave it there on details tab, you'll have this problem. either close task manager or switch to another tab.