You could implement "Cloud Saves". Upload the savegames to an online webservice. You can access a webservice from Unity via the class UnityWebRequest. There are countless technology options for implementing a webservice on the server-side, and which one to use depends on personal requirements, preferences and skills. So I will leave this choice to the reader.
In order to permit the player to access the same savegames from multiple devices and web browser, you need to give them personalized account with username and password.
This also gives you the advantage that all the savegames on your own server give you lots of information about how your players play the game, which you can data-mine to find out if your game works the way you intended. But it also means that you need to have a privacy policy and might need player consent for storing and analyzing their savegame data (just storing the savegame data for the user and never looking at it seems to me to fall under "legitimate interest" and thus would not require explicit consent, but IANAL).
Unfortunately, this means that you are now responsible for keeping that savegame webservice running indefinitely, or the game becomes unable to save which could render it unplayable. So in order to still keep the game playable when the server is offline, you might still want to use PlayerPrefs as the primary source of truth and synchronize the data stored in PlayerPrefs via webservices when possible.