wordpress Mixed Content: error and login page redirection to main url

I have uploaded the plain wordpress directory to server (Github and Jenkins) and have in config file:

define('WP_SITEURL', 'https://maindomain.tld/sub');
define('WP_HOME', 'https://maindomain.tld/sub');

My problem is I am still not able to login into my dashboard as it gets redirect to main url https://maindomain.tld/login.php with

default backend - 404 error

Another error is when I visit home link https://maindomain.tld/sub in console I see Mixed Content error.

Are these both errors related to each other if it is or not How can i solve this?

Thanks for the help.