The Callisto Protocol

Microtransactions in The Callisto Protocol are summarized as...

The game is singleplayer only and features no direct microtransactions. It does have several planned DLC, none of which are out yet. All of the DLC contain new content as well as some cosmetic items in the form of skins and death animations. The DLC can be purchase individually or via a Season Pass, at which point you're purchasing unknown content that will be available at a later date.

The season pass is currently only available as part of the Digital Deluxe edition. The Digital Deluxe edition also features some unique character and weapon skins. There is no way to buy these skins separately.

Additionally there are several DLC packs available which feature nothing but cosmetic rewards, some of which are special kill animations.

The game contains many smaller DLC packs that contain (almost) nothing but cosmetics.
Contains one or multiple Season Passes, encouraging the purchase of unknown DLC you might never have purchased otherwise.