Endgame mythic items can be obtained only in raids with friends and you can't use your own other characters to do them solo. You can't find a party considering low online numbers and most of them from China. So Co-op isn't optional for endgame content it's mandatory.

I read in-game guide and made some items but can't get urn system.

What are those urn resources in the upper right corner, I mean red stick and smth else, where to get them? What they do?
Where to check available urn pages for inscribe?
Why I can't add a legendary weapon from my bag inventory for my spirit weapon?
Why we don't allowed to do set spirit items but only legendary?
How to make smth useful and not trash compared to raid items in the urn?
Why in a guide there are no examples for those items and spirits it describes?
What is growth potential?
Can you add more spirits to your spirit weapon without extracting spirit from it thirst?
What about buttons like 700/20 idk what they mean and those numbers? There are no tooltips too.
Where to find some spirits I like and set as preferred to farm them?
Why spirits come in quantity 1-5 in a stack and similar stacks don't stack?
Is there a difference between 50 and 150 lvl urn dungeon in a spirit quality or types?
The whole system is a fatal mess.
The game was something complex before but now it's a mess and most systems aren't in any guide and no tooltips for buttons.

Not enough inventory space. Still 4x56 shared slots.

Some text (item descriptions, etc) don't translated in English

If you can stomach the AI use this is a very good idle incremental with a lot of fun features. The english translation is a little rough at the time of writing but it's more than adequate to enjoy the game.