Microtransactions in The Finals are summarized as...
The Finals is a free-to-play game with a large array of cosmetics which can only be obtained through the purchase of a premium currency by the name of Multibucks. This premium currency can largely only be obtained with real money, but the free Battle Pass does reward it as well in very small quantities
The Battle Pass can only be obtained through the use of Multibucks, but it also features a free tier. The Battle Pass rewards enough Multibucks to purchase the next Battle Pass, but only through the Premium Pass, the free tier rewards barely any premium currency, and saving up will take years to earn enough for a single Battle Pass.
Multibucks comes in several quantities, while in some cases their quantities match that of store items, in most cases they don't. Cosmetics come in all shapes and size, from skins, tiny weapon stickers, reload animations, and charms, to emotes, pets, and many many accessories. If there exists a real-life something, there's an in-game equivalent something. Some of these cosmetics are tiny and would be hard to notice in regular gameplay, and yet they cost a very large amount of money.
Many of the cosmetics can only be purchased in bundles, with no way of purchasing individual items. This forces you to spend way more money than you otherwise would have just to receive the individual item.
Besides the regular purchasable cosmetics the game also features a daily rotating store as well as seasonal or event specific cosmetics, preying on your to buy it as soon as possible, so you don't risk losing out on that "exclusive" item. This rotating store largely features bundles, with no way of purchasing individual items.
The game also offers some free cosmetics. These are earned through regular gameplay, mostly through leveling up your character or by using individual items for a certain amount.
While the game is free-to-play and features no pay-to-win elements or other paywalls, if you wish to have any sort of player expressions through cosmetics, you will need to spend a lot of money to stand out from the crowd.