I have a question about Stripe BLIK payment.

I see in Stripe's documentation that BLIK payment is possible (Payment methods types -> Bank redirects->BLIK). Is BLIK payment possible in FormNx using Stripe as indicated in their documentation?

All payment methods supported by Stripe should work in FormNX stripe integration.
FormNX simply sends the details of payment to stripe & from there stripe will collect payment in whatever method you select.