Ava here from Shopify.
You can offer a payment plan to your customers with the help of an app. At the moment, the admin section does not have the functionality to offer partial payments, so an app will be needed to add this extra option. There are some popular options here such as Lay-Buy, Partial.ly Payments and Parcelamento ‑ Installments. There is a full range of apps here though!
Also, you can check out some of these apps that allow for partial payments on a subscription plan. They may also be useful for you!
Let me know if you have any more questions, happy to help!
You can use Klarna, it facilitates payments in 4 installments and with no added interest. Although it's not at checkout but rather inside the product pages, (which in my opinion is more convenient, as it shows the personalized amount of each installment based on the product's total price).
These days you should facilitate everything as much as possible to work on the UX.