@VladAdmin Thank you for reaching out. Happy to answer your question.
You have an interesting ask on automatically moving Azure backups to Azure Immutable blob. Currently, Azure backups to Azure Immutable blob is not supported. The feature is on the roadmap. However, there is no ETA to share as of now. I encourage you to leave your valuable feedback here - https://feedback.azure.com/d365community/forum/153aa817-0725-ec11-b6e6-000d3a4f0858 The more individuals that vote for the request, the higher the likely hood it will be implemented.
Alternate option as of today is Multi User Authentication (MUA) - https://learn.microsoft.com/en-us/azure/backup/multi-user-authorization#:~:text=Multi%2Duser%20authorization%20(MUA),performed%20only%20with%20applicable%20authorization. however other solution which you are talking about will ultimately change the approach of taking backups
----------------------------------------------------------------------------------------------------------------------
If the response helped, do "Accept Answer" and up-vote it