Cross-Platform Multiplayer Development Help

I want to make a game that supports multiplayer matchmaking cross-platform between as many platforms as possible (PS4, XBox, Windows, Linux, Mac, Mobile, Nintendo, etc.).
I want to allow for in-game item purchases.
I want each item to be linked to an account that can be used independent of a platform.

To narrow down my problem, I am in search of matchmaking software or services such as Steam, Occulus, or GameSparks. I did some reading and it appears that Steam is not compatible with PS4 for example, but I could be wrong. I like how Fortnite has the idea of an account that is separate from a PSN account. If I am not mistaken, it is just an Epic account that is linked with a PS4, XBox, or some other account.

Any help, tips, ideas, or guides towards achieving this goal would be greatly appreciated. Thanks.

My understanding is as follows.

You are going to have to write most of the stuff yourself. The idea here is to use your own account authentication system and then have all platforms use that.

You would also have to write your own matchmaking and server browser system that uses standard UE4 features and not specific features for Steam etc.

I would pretty much write everything to run on a secure RESTful web-service and drive everything from that.

has there been any development on this?

There has been no development on this on my end yet.

It appears that Epic might be providing the answer to this here:

no. ■■■■■■. way. Unreal Engine just. got. BETTER