I have written a step-by-step manual demonstrating how to install, backup, and upgrade Moodle 3.9 LTS on a self-hosted Ubuntu 20.04 LTS server.
The guide only assumes you have a publicly accessible server (with a static IP address) and a domain name. Some Linux familiarity may be helpful too. While I don't cover how to install Ubuntu, this is fairly straightforward, and I also figure most people will use cloud images instead.
I'm not really sure how to get it out there yet. I may end up publishing it on a website. I am also considering making a complementary screencast of me following through the procedure. If I make it, I'll link it here too.
I would welcome feedback if anyone disagrees with any part of it.
A 'restoring site from backup' section is a work in progress.