Visvanath Ratnaweera

If you referred the chart Ken has given, you'll know that Moodle 3.8 to 4.1 are compatible with PHP 7.4.

MariaDB 10.3 is a different story. I'll leave it to you as an exercise. The information is there, in the same chart.

P.S. You might want to tell the Italian community https://moodle.org/mod/forum/discuss.php?d=442963#p1780728 that you are getting answers here in the English community.

The standard Moodle message "boxes" are per user. Therefore not associated to courses. The additional plug-in Mail https://moodle.org/plugins/local_mail claims to do that. Never tested myself.

It depends on how the web server is configures and Moodle too. If the web server serves HTTP for that domain, you should have $CFG->wwwroot='http://YOURDOMAIN'. if it servers HTTPS, then $CFG->wwwroot='https://YOURDOMAIN'.

Well, a back-and-forth between these two can cause havoc, since many things get cached in the server as well as the client. So try with another browser, another computer.

And the only problems is the "insecure" warning? That comes from the browser. You can accept it and move forward.

If you get it halfway running, try to run https://docs.moodle.org/en/Moodle_migration#Update_links_containing_wwwroot_in_the_database.

If nothing helps, switch on https://docs.moodle.org/en/Debugging and get a full trace.

P.S. It is never too late to read the documentation, https://docs.moodle.org/en/Moodle_migration.

P.S. Generally, I avoid exposing the real domain and the IP address of Moodles falling sick.

;)

I get the login screen by visiting the "Log in" link, yoursite/login/index.php.

What is the format of those documents? If text files, consider a versioning system like Git. If Microsoft DOCS, LibreOffice ODT, Goodle Docs something, etc., then check in relevant forums. If some sort of a HTML, then the closest thing Moodle offers is the standard https://docs.moodle.org/en/Wiki_activity.