I switched my bucket from fine-grained access permissions to uniform, to try out managed folders. The UI assured me that I have 90 days to change back to fine-grained:

All object access is controlled by bucket permissions and objects cannot have their own access control lists (ACLs). To allow per-object access, you can switch to fine-grained access within 90 days.

But when I do, I get an error:

Unable to update access control. Invalid request for a uniform bucket-level access resource

What can I do?