Would anyone know how to solve this problem?
The platform I run it from and redeemed it for free is GOG GALAXY.
When I finish the game the save files are there, and in the launcher it tells me I'm at 5%, then when I start it it doesn't load the saves and me it always restarts me from 0

There's a "save slot" chooser in the main menu; maybe fiddle with that?

Note: with saves working well, you still start at the central tower where you began the game the very first time, every single time you load the game (so it doesn't save your "position", nor the specific orcs you just killed - those swiftly get replaced with new ones anyway) - but the available quests, knowledge of the various captains, available runes, etc, etc reflect what you've done in the game up to that point.