Please install and activate the plugin “SSL Insecure Content Fixer”.

Under the settings of the plugin “SSL Insecure Content Fixer” please select the item “Simple”.

Under “HTTPS detection” please select HTTP_X_FORWARDED_PROTO (eg load balancer, reverse proxy, NginX)

Now under Wordpress Address (URL) and Site Address (URL) you can specify the blog URL with https under the general settings of Wordpress.