Hash_hkdf(): Argument #2 ($key) cannot be empty

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I know there is a bug #34012, but it is closed, I read everything and I cannot understand what I should do to solve the issue. I have the secret in the config.php, the proble persist. What is the solution?

Thank you

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Nextcloud version : 28.0.5
Operating system and version Ubuntu 22.04.04 LTS
Apache or nginx version (eg, Apache 2.4.25): Apache 2.4.52
PHP version (eg, 7.4): 8.1

The issue you are facing:
Continuous error in the log
hash_hkdf(): Argument #2 ($key) cannot be empty

Error while running background job (class: OCA\DAV\BackgroundJob\EventReminderJob, arguments: )

Is this the first time you’ve seen this error? (Y/N):
N
Steps to replicate it:
Nothing special, they are always there

I have exactly the same issue. Do not understand it. It is constantly in the log.