Returnal developer Housemarque has released a new patch, 1.3.4, for the recently released PlayStation 5 exclusive that would seem to resolve the issue introduced with the previous patch that essentially broke the video game. The developer even had to pull the previous patch, and the new one essentially just reverts the title to the previous stable 1.3.1 build while also fixing an issue with trophies as well as keyboard exploits.
That said, there is no guarantee that those folks that experienced problems with the previous patch as some saves will be recoverable while others will not. You can check out the official guidance from Housemarque for those that had issues with their saved games after Returnal Patch 1.3.3 below:
Some game saves will have become corrupted with Patch 1.3.3, but maintained their file size. Players with those save games are able to safely continue their progress after installing Patch 1.3.4, without the need for using a backed up save game.
Unfortunately other save games will have been effectively "deleted" by Patch 1.3.3, with their file size reducing to 0KB. These save games are not directly salvageable by Patch 1.3.4, without a backup save game available.
In those cases, please try using a backed up save from PS+ if available, after installing Patch 1.3.4. With an intact save game from PS+, players can safely restore and continue playing with Patch 1.3.4 installed.
Depending on the console settings, the cloud save may have been overwritten by the "deleted" save game noted above. If this is the case, progress will remain unsalvageable, even with Patch 1.3.4.
Returnal is now available for the PlayStation 5. As noted above, the latest patch reverts the title to a stable state in order to make saved games safe to play again.
Related Forum: PlayStation Forum