Solution for users who are using nextcloud default app that is stored in IX.applications folder
steps:
1) ssh into your truenas server
2) use the command to go to the folder where the config.php file is kept:
cd /mnt/.ix-apps/app_mounts/nextcloud/html
3) Verify that the config.php file is there:
ls
4) use nano to edit the config.php file with the following command: (if you don’t use sudo you wont be able to save the file)
sudo nano config.php
5) look for ‘overwrite.cli.url’ => and ‘overwritehost’ =>
6) alter the above lines with your domain as seen below:
‘overwrite.cli.url’ => ‘my.domain.com’ and ‘overwritehost’ => ‘my.domain.com’
7) save and exit the file
this website helped a lot https://docs.nextcloud.com/server/stable/admin_manual/configuration_server/config_sample_php_parameters.html