Need basic help with logfiles

I set up Nextcloud on Open Media Vault via Docker/Portainer last week. (OMV installed on top of Debian minimal).

Sync performance has so far been poor. Files are present and marked in Windows File Explorer as synced, for instance, even though they have been deleted from the server via the web UI and should have been removed from the Windows client too. Larger files (10GB+) struggle to sync in both directions.

I’m trying to look into why, but I’m finding Nextcloud’s error messages generally not helpful. Specifically, I’m struggling to even identify which logs Nextcloud is instructing me to check.

In Windows, I open the NC client, press F12 for log output and and pointed to a temp directory; the directory is empty, however.

On the server, …/data/nextcloud.log is present and detailed, but the entries seem only to relate to email (“Connection could not be established with host :stream_socket_client(): unable to connect to”), which seems odd as email was working fine, but I removed the account as I prefer Mailspring’s layout/dark mode to the Nextcloud email one.

Where else should I be looking for file sync-related log files, both on the client(s) and the server?