How to get around "access through untrusted domain" error

https://docs.nextcloud.com/server/18/admin_manual/installation/installation_wizard.html#trusted-domains-label

https://docs.nextcloud.com/server/18/admin_manual/configuration_server/occ_command.html#config-commands

You can use OCC instead of manually editing the config file. The config file is located in the config folder under the Nextcloud web root.