Mortar zips your saves before it changes them: before a profile update, on every game start with Back up saves before Play, and on a timer with Scheduled save backups (both under the game's Save backups in Settings). A game whose catalog entry has no save folder shows no Saves tab, no Saves card on Home and no Save backups page.

To restore, stop the game, open the Saves tab, choose Save backups…, pick a backup and choose Restore. Mortar backs up the current Saves folder first. Open backups folder shows the zips; Backup location in the game's settings moves new ones. For Valheim, The Sims 4 and Vintage Story the list also shows the game's own copies, marked Kept by the game.