Nextcloud SQLite Troubleshoot & Repair

I have a self-hosted Nextcloud instance running in Docker. Initially, it was set up using SQLite as the database backend. I'm currently facing issues accessing the instance, and I suspect there may be problems with the database configuration or data migration.

I need a reliable expert to:

Inspect and repair the current setup to get Nextcloud working again with the original SQLite database (data is very important — personal photos, etc.).

Ensure that the application uses the correct owncloud.db file and that no data is lost or overwritten.

Diagnose and resolve any internal server errors or misconfigurations.

Ensure proper configuration in config.php and other critical settings.

Optionally: advise on or prepare for a safe migration to MariaDB, but only if 100% data-safe.

Environment:

Docker-based setup

Nextcloud 31.0.2.1

SQLite (owncloud.db)

Access to server via SSH

Apache, PHP 8.3, Redis, APCu

What I provide:

Full access to the server and Docker containers

Relevant logs and error messages

Current config.php and database files

Deliverables:

A fully working Nextcloud instance using the existing SQLite data

Confirmation that no files or user data were lost

A short report on what was fixed and how

Optional: steps for future migration to MariaDB if advised