Easiest would be to run an S3-compatible object storage app such as minio.
It’s an old tutorial, but it should still work.
Depending on your needs, you might want to add more than 1 instance, in different, close-by, regions, to replicate your storage.
I don’t have a turnkey solution unfortunately. We are planning on eventually providing a S3-like object store, but not for a little while!