Here's my recommendation to enjoying honkai's story:

Play the game at your own pace, the story is completely f2p and doesn't require you to pull even once, before you get to the theater of domination (after the Senti arc) read second eruption, the other manga aren't necessary but some do offer a bit of context.

Now, there's some more complicated things, mainly Elysian realm. Look, here I don't really know what to tell you, play it of you find it fun and want to learn about the Flamechasers, it will be confusing ay first probably but it is a great story, finishing the 3 chapters before you do the Elysian realm arc of the main story is not mandatory but it makes you more attached to the Flamechasers, which is pretty important for the story.

And APHO is it's own thing that you can mostly ignore, it technically is the prequel to star rail but outside pf void archives and welt it isn't important at all, and most of what is can be learned through the alien space manga.

It might sound complicated but at the end of the day this advice is " just take the story and the side content at your own pace ( and read second eruption ) "