Microtransactions in Diablo Immortal are summarized as...
The game is primarily a mobile game but it is available as a PC game as well. The PC game still includes all of the predatory monetization you would expect from a mobile game.
The game contains multiple currencies, two of which can be obtained directly via real money purchases. One of these is called "Eternal Orbs". Eternal Orbs come in odd bundle sizes that force you to over pay for things you might want. This currency is primarily used to buy cosmetic items but also for some in-game benefits.
The other currency is called "Platinum" which can be obtained with Eternal Orbs or through other means such as the Battle Pass or in-game daily quests. This currency is primarily used for player to player trading.
Additionally some shop items can not be purchased with either Premium Currency and instead have to be purchased directly with real money.
After clearing content in the game you might receive popups offer you a deal for real money that allow you to receive better rewards from the content you just did. These popups can range from a couple of dollars to even 100 dollars.
Diablo Immortal features a Battle Pass that has 2 premium options as well as free rewards. The extra premium battle pass option instantly gains you a few levels in the battle pass but it also rewards unique cosmetics. Levels in the battle pass can be purchased using Eternal Orbs.
The game features a subscription service that primarily rewards you with quality of life improvements such as bigger inventory space and remote player market access. These also offer you daily login rewards that you don't get if you don't log in every day, even though you paid for it.
Technically most non cosmetic items in the game can be earned without paying anything. But in reality this is highly unlikely. Lots of high level items require you to get incredibly lucky over and over again. Instead of getting lucky you can pay money to guarantee these items to drop, but even then many items will be obtained randomly through a lootbox like system. So even spending money does not guarantee you will receive the items you are after. Many of these items gain you power that puts you at a significant advantage over other players. Especially the first few years of the game.
Obtaining the best gear in the game will cost you a very large amount of money or many years of playing. On top of that there are multiple cosmetic items you can purchase as well as a subscription service. If you plan on playing this game do it with the knowledge that you will be severely behind other players in terms of power, or join them and spend loads of money.
Worth noting as well; You can create multiple different characters. If you purchase cosmetics on one character they will NOT be unlocked on other characters, even though it is on the same account. The only thing that is shared between characters is the premium currency Eternal Orbs.