I remember reading an article regarding legal requirement of shipping Li-ion batteries - they should be at 40% charge level.
In practice, the best voltage level for storage is 50% ~ 3.7V.
Batteries I’ve received tend to be various states of charge from 3.5V to 3.7V.
If I intend on using the battery within the next week I fully charge to 4.2V otherwise I put all new batteries onto charge up to 3.7V, check the internal resistance then pop them into a battery storage container until I think I will be needing them. Then they are onto the charger to 4.2V.