Hi @jicho, I am sorry you are having trouble.
Unfortunately I don’t have a Synology system and don’t know how one would deploy n8n on it.
Is there a chance you were using a custom n8n image in your docker setup? I am asking because your n8n instance seems to run as the root user based on the UserSettings were generated and saved to: /root/.n8n/config line. The standard n8n image would run as user node though (and has been for quite some time, even on previous versions).
If so, you might need to update the configuration in your system, similar to what has been described here. If that’s not it, can you confirm which command/docker compose config exactly you are using to run n8n and where your SQLite database with the workflows lives?
Can you also confirm from which version you have upgraded?