Hello Dmitry Maksymets,
Welcome to the Microsoft Q&A and thank you for posting your questions here.
I understand that you are unable to setup Azure Database for PostgreSQL Flexible Server.
With
(InternalServerError) An unexpected error occurred while processing the request. Tracking ID: 'fdeae066-da8b-4c8d-b1cd-36cccb71a4e1'
is a backend Azure service error. It is not caused by your misconfiguration, and retrying or switching methods (UI/CLI) does not guarantee success. This error is transient and often linked to regional capacity issues, especially with burstable SKUs or v5 SKUs.
You can try again later and raise support ticket via your Azure Portal or use Priority Customer Support - (PCS).
I hope this is helpful! Do not hesitate to let me know if you have any other questions or clarifications.
Please don't forget to close up the thread here by upvoting and accept it as an answer if it is helpful.