Documented the save transfer process for anyone interested while "porting" Zips's save. This is for Save Wizard, those who are savvy enough to use PS4 Save Mounter on a jailbroken console can just skip to step 6/7 after retrieving their decrypted save, I won't explain all of that here.
- Backup your desired HZD save (it probably needs to be the complete edition or a version that could technically access the DLC expansion) to a USB drive. Sony instructions
- Open Save Wizard on your PC and insert the USB drive
- Choose the desired save under "My saves", right click and select "Advanced mode"
- Wait
- Once you see the hex view, click on "Export to file" (second to last icon in this pic: https://abload.de/img/bildschirmfoto2020-08glk1t.png)
- Keep the name "checkpoint.dat", it's used in the PC version as well
- Navigate to C:\Users\<username>\Documents\Horizon Zero Dawn\Saved Game and pick a save folder. There must be an existing save in the folder that you're going to overwrite. I used autosave0.
- Launch the game and load the save (the text and image you see won't be representative of the PS4 status). Should load just fine.
- You may want to immediately save your game to a new manual slot to create a more proper save state.
- You can now quit Save Wizard and eject the USB drive, you're done
Note 1: I ran into a weird issue where the game took it's mirroring/blurring in 21:9 mode ad absurdum and applied it to gameplay as well, but restarting the game fixed that. It was probably not related to the PS4 save, but just the general jankiness of the PC version. I also had a single crash while fast traveling across the map, but that also wasn't reproducible and might just be due to the state of the port.
Note 2: I haven't tested this extensively, so there might actually be issues. Use at your own risk.