Really want to backup it before starting playing and spamming my name all over.

UPDATE [HoMM 3]: SOLVED
HiScore.dat file gets created in \Data sub-folder after the player gets on high score table. Before that moment there is no such file there (source of my inquiry) and the game displays hard-coded default table instead.

Which game?

HoMM 3

My bad hehe :)
Turned off PC and head hit the pillow when I realized I left that piece of info out.

According to this, it's /Data/HiScore.dat
https://www.celestialheavens.com/forum/4/9242

I actually found that post before posting here, lol. But thanks!

At present \DATA folder is just handful of files that, to me, look like archives containing many small files (from my binary inspection). I even did a search and best match was "HISCORE.FNT" inside the 100 MB "H3bitmap.lod". Not much help there. File structure probably got changed by the expansions (post referred to vanilla HoMM 3) or by GoG themselves.

For now I'll just take a screenshoot of the intact pristine high score. It will have to do because I'm getting impatient about holding of my playthrough because of it :)

Maybe the original high score is hard-coded until the player naturally modifies it - then a proper files gets generated and used from then on. I have just now found a "HiScore.dat" mentioned in the main executable so there might be some merit to that theory.

That's actually quite possible.

Ok, finished the Tutorial and put my name on the high score only to have the mystery file appear in \Data. Updated 1st post.