HeneralOwel: yeah, I already figured it out a few hours ago. The next-gen version was released earlier on console that's why I wasn't able to do it. now that it's released on PC, the cross progression was already available and it transferred smoothly. thanks!
murad394: Were you able to transfer from PC (Steam or GOG) to PS5? How?
According to GameSpot you cannot do that! Only PS4 <-> PS5 (which I tested), or PS5 to PC.
I'm downloading the update on Steam atm.
I also sought GameSpot advice first and I thought there's no hope, but thankfully they are wrong.
I updated both PC and PS5 versions of the game, so now both are running the next-gen version.
Since my PSN acct is linked to my GOG, I loaded my save file on PC. then I hit options, went to "Save Game", then at the bottom right it says "C" for Cross Progression. I hit "C" and it gave a dialogue box that says that save file will be uploaded to cloud save. Then a cloud icon appeared at the right side of the save file which indicates that the save file is already in the cloud.
then on my PS5, I selected 'load game', and the save file from GOG is already there. I loaded that save file and it worked smoothly.