The short answer is - you can’t. The encrypted data are tied to your encryption key for your account on the server, which you don’t have direct access to.
Having said that, if you installed your software to a Synology NAS then you aren’t running Bitwarden software. Rather, it is software coded by a developer that has no association with the Bitwarden project and has cleverly made it look just like you were running an actual instance of Bitwarden - essentially a Bitwarden imposter. So who knows - maybe it is possible on the software you have installed to your NAS?
so more vaultwarden
but the exported file is still named bitwarden_encrypted_export_2022
so meaning it could be opened under a local bitwarden system under windows i guess.
It’s more for safety reason in case my nas is down of any reason
If you have confirmed you are not using Bitwarden’s software, then this is probably the wrong community to approach for answers. I suggest you reach out to any support channels for the developer of the imposter software you installed, if they exist.
As such, I am going to close this thread now, but feel free to DM me if you have questions about that.