Hi @DianaSM Thank you for posting your Question on Microsoft Q&A and for using Azure services.
Long term back up retention in Azure SQL Managed Instance and Azure SQL are already in General availability since December 2021.
Long term back up retention for Azure SQL and Azure Managed Instance
With the feature still in public preview, is there a possibility that our backups will lose if changes to this feature occur before the general release
I think you should be fine for your Azure DB backups.
Let me know if you have anu further queries