Until *very* recently, PS4 did not have cross save availability with PC and mobile devices. It is, however, a feature added in the 2.0 update a few weeks ago. To do so, you must sync the game account with a Mihoyo Labs account.
On the account you want you want keep, go to the title screen and select settings.
Select user center
And finally select Link Account.
This will allow you to link the game to a Mihoyo account if you have one or create a Mihoyo account if you don’t.
After this, the next time you log into Playstation to play Genshin, you need to actually create a new Playstation account with a new email (yeah, it’s a drag) and it will ask you when you turn it on if you have a mihoyo account to link.
It’s easier to do the opposite direction, from PS to a PC/Mobile account, as you can more easily change email associated.