Encountered a strange issue where the game created an empty directory instead of a save file with the ".TheWitcherSave" extension, and the game would hang until I force-closed it. Directory was named as a proper new save file would be. It had saved 50ish saves in the past few days with no issue, however. Exact same PC, exact same GPU drivers, etc.
Folder has both read and write permissions for "Everyone", Defender wasn't protecting the directory, tried a fresh install 3x (including wiping mydocs' save and appdata files), tried windowed, tried vsync, tried all compat. modes, ran as admin, disabled fullscreen optimisations, removed all saves and tried to a start new game, no mods were present, deleted temp files in appdata directory (both between launches and after loading game), save cloud was disabled, tried all possible configurations of forced GPU render and display settings, and no cigar.
It stopped working after doing a bunch of stuff, but one of which was touching the game application's settings in my GPU manufacturer's 3D application control software (for the first time). I'd toggled all options in here to all possible combinations, but I finally reinstalled another version of the graphic drivers (a clean install, after removing all drivers in safe mode) (for my RX 5700 GPU), and this time DID NOT TOUCH the GPU's interface at all.
Now it works. Somehow the GPU drivers were forcing the game into an error which made the game hang and create a directory where it should have created a save file of the same name (though with the proper extension).
No idea how the f that makes any sense, but I'm just glad it works now - even with my old save files. Posting in case anyone else encounters a similar issue.