You can still mount an object storage bucket to the filesystem, but it's not supported officially by Immich and you anyways have additional delay caused by the fact that your device reaches out to your server, and your server reaches out to the bucket.
It would be amazing (and I've been working on that) to have an Immich that supports natively S3 and does everything with S3.
This, together with the performance issues of Immich, is what pushed me to create immich-go-backend (https://github.com/denysvitali/immich-go-backend) - a complete rewrite of Immich's backend in Go.
The project is not mature enough yet, but the goal is to reach feature parity + native S3 integration.
Our quickstart.sh[1] bundles Minio, but you can configure Ente to use RustFS[2] or Garage[3] instead.
[1]: https://ente.io/help/self-hosting/#quickstart