You’re wasting your time troubleshooting an installation method that’s not officially supported by Nextcloud.
It also installs an outdated version (Nextcloud 29), which reached end of life back in April 2025.
Even if you manage to fix your current issue, the very next problem you’ll face will be upgrading to the latest stable release — currently Nextcloud 31.0.9 — which is a major jump with a lot of breaking changes.
If you’re running Proxmox, you have much better and future-proof options:
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A clean bare-metal VM installation (Ubuntu/Debian)
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A Snap installation (Ubuntu/Debian)
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Or the officially supported Nextcloud AIO provided directly by the Nextcloud team
I’m using Proxmox with Nextcloud AIO myself.
I’ve written a complete step-by-step deployment guide (with explanations and maintenance notes) showing how to set it up properly:
Proxmox + Nginx + Nextcloud AIO + Watchtower deployment guide