IMO Stripe API[^1] is following well the REST principles and constraints. Btw, if I well remember, they are not using PUT at all while they obviously allow users to update some resources.
They implemented an "Idempotency-Key" header that you could maybe call a "shortcut". Although it's not really deviating from HTTP standards. I guess it was easier and more pragmatic for Stripe and users to implement an "Idempotency-Key" header instead of duplicating each POST endpoint with PUT and PATCH methods since they also allow partial updates. I guess (again) that they would also have to use/implement additional header (such as ETag or If-Match) to replicate current "Idempotency-Key" header behavior.
Disclaimer: This last paragraph is full of assumptions and I most probably miss a lot of internal details from Stripe API.
They implemented an "Idempotency-Key" header that you could maybe call a "shortcut". Although it's not really deviating from HTTP standards. I guess it was easier and more pragmatic for Stripe and users to implement an "Idempotency-Key" header instead of duplicating each POST endpoint with PUT and PATCH methods since they also allow partial updates. I guess (again) that they would also have to use/implement additional header (such as ETag or If-Match) to replicate current "Idempotency-Key" header behavior.
Disclaimer: This last paragraph is full of assumptions and I most probably miss a lot of internal details from Stripe API.
[^1] https://stripe.com/docs/api