Synchronizing your Hades 2 progression from Steam or Epic Games with your Nintendo Switch 1/2 is easy!
All you have to do is load up your game and go to the Cross-Saves section of the menu.
Upon clicking it, you'll be asked to enter your login info for your desired platform.
Depending on your settings here, you'll likely have to validate through an email code or some other verification method.
Once connected, be sure to Sync & Quit after each session on your Nintendo Switch 1/2.
After doing so, you should be able to continue on from the same progress when you hop back to playing from either Steam or Epic Games.
Will there be cross-save progress for the PlayStation or Xbox release of Hades 2?
As of now, this has not been confirmed. However, note that the first Hades ONLY had cross-progression with the Nintendo Switch.