Boon of Saving Grace (5e Epic Boon)
From D&D Wiki
Boon of Saving Grace
Choose two ability scores for which you lack proficiency in saving throws; you become proficient in saving throws with these abilities. Then choose one ability score for which you are proficient in saving throws; You gain expertise in saving throws with this ability score.
If you already had proficiency in 5 or more saving throws, then any extra proficiencies granted by this boon can be exchanged for expertise with another saving throw.