Another under-documented process.

1. On your Vita, you need Save Manager Plus (not savemgr) to export decrypted saves. Load that homebrew app and export/decrypt the desired saves.
2. This info is only in the fucking changelog but the directory SaveManagerPlus puts your decrypted saves in is at ux0:data/vitaSaveManager. So copy them from there to your PC.
3. Start the same game on Vita3K and ❗️get far enough to create a new save, save the game, and close it. From there you can right click the game in Vita3K and click “Open Folder > Saved Data” to open the saves folder in your file explorer.
4. You should now have the slotparam file and a data file named like SAVEDATA0000.DATor USR-DATA0000 but ❗️you can only import saves by replacing that new save data file generated in Vita3k, I think because it correlates to something in the slotparam. So if you’ve generated a new SAVEDATA0000.DAT and expect to be able to import and load SAVEDATA0050.DAT (a decryped save from your Vita) alongside it, it won’t be recognized. ❗️You have to rename the decrypted save you want to import to the one generated in Vita3K and replace it, SAVEDATA0000.DAT in my case.
5. By replacing that file, your save will show up in Vita3k. ❗️However, it seems that the metadata about the specific save is stored in the slotparam file so, for me, the information about the slot in the in-game save data load screen was wrong –❗️it looks like it’s still the beginning-of-game data you created, but once you load it it’s your imported save. So just create a new one ASAP.

Contact me if this process stops working on newer Vita3K versions.