I am not the DM of this group. A new player (new to our table, but also new to D&D) joined two sessions ago and is playing an artificer (level 7). I noticed in the first session that the player didn't really know how to play, and the DM didn't explain anything (like how to cast spells, or any basic rules like that). In session 1 the player didn't know what spell preparation was, and the DM kind of hand-waved it. The player cast a 3rd level spell and something wild magic-y happened. I actually messaged the DM afterward about casting the 3rd level spell and he gave me a vague nothing response about it. Session 2 the player once again didn't do any spell preparation, cast more 3rd level spells, and more wild magic stuff happened, enough that the artificer is some kind of homebrew wild magic artificer. The player hasn't really used any artificer infusions, flash of genius, etc.

It's the DM's purview to do whatever homebrew they want, but should they tell players about it? And can I ask the DM to show me the actual homebrew class so I can understand wtf is happening? This game often feels like total Calvinball. A few more examples: I prepare from a list of spells, but another PC wizard doesn't and just kind of casts whatever is on his character sheet. Certain spells that require monetary components (Divination, Glyph of Warding) aren't enforced (I do track and spend for Divination, but the Glyph of Warding PC doesn't).

When I DM my own groups I always ask their approval for major homebrew or house rules in advance ("hey let's vote on this house rule about attunement") or just tell them if it's an insignificant house rule ("hey I'm going to homebrew that the paladin can ritual cast like a cleric"). When I signed onto this game it was described as "rule of cool" but also "pretty much normal D&D without any major homebrew".

tldr: how much Calvinball is too much Calvinball, and is it none of my business what my fellow PC's homebrew class features are?

Edit: I messaged the DM to ask and he said we would be discussing it at the next session. So that's a start I guess.