Where to find the master key for backup?

I’m looking for a way to backup the encryption keys as mentioned in the documentation. I’m using an S3 comatible external storage as primary storage and there are no encryption keys in the data/ directory.

According to this bug report, the recovery option mentioned in the documentation is not available by default because Nextcloud uses a master key.

My understanding is that I need to find this master key if I want to be able to decrypt my files in case of server failure. Where can I find this key?

I’m using NC16 installed via snap.