as long I get your setup right you have nginx reverse proxy in front of your Nextcloud application (native, docker etc…).
for such setup you need nginx to provide right http header x-forwarded-for, x-real-ip etc… and Nextcloud application must trust this headers from (trusted_proxies) so the application knows the request doesn’t come from {reverse proxy} and was originally send to {trusted_domain}
means your Nextcloud application doesn’t understand the request was originally send to {trusted domain}…
I still don’t fully understand your setup… but maybe this WIKI helps you to find good starting point Apache Docker behind reverse proxy