As the title says. Any idea (maybe in a config file somewhere) how to point the game at those already existing saves?

OK. This is strange, but it worked. I backed up the saves. Uninstalled the game completely ( including deleting the Wizardry 8 folder). Reinstalled the game. Added back the Saves folder. Still no luck. I then installed the fan patch Wiz8v128 and launched the game from there and the saves were back. If I use the vanilla launcher, no saves. I have no idea why this happening, but at least I can still use my existing saves, now.

I guess you have installed the game in an uac protected folder, like program files etc?
If so move it out to a neutral folder, e.g C:\games\wiz8,
that should prevent windows from rerouting the saves to a protected folder where the game cant "see" them.

However, 1.28 uses a slightly changed format for the save,
it can read the 1.24 saves and will convert save data to its a new format on next save,
but ofc 1.24 cant read that format, so once you changed to 1.28 you are stuck with it in that run
until you start an entirely new one with 1.24