What is the safest way to leave my MacBook on 24/7 with macOS Mojave?
I'd say "Nothing".  Assuming there is an defective battery, you can't 'manage' its safety with any specific behaviour. It could fail and overheat while in use, or while charging.

The odd recall notwithstanding, Apple has worked very hard at making laptops use minimal power when closed, while also allowing some necessary background tasks; and then letting them spring back to life when you open the lid.

Modern SSDs use a fraction of the power of the old mechanical hard drives that needed to be spun down to save energy.

I rarely turn off my 2014 MacBook Pro, and only reboot it when updating the OS or troubleshooting.