How to turn OEM on in e.os

I’m trying to turn on OEM in e.os on both the S9, Pixel 5 and Lenovo Yoga Tab 3. However, there is no option on all 3 devices.
I would like to install TWRP and / or update my e.os manually. However, every installation guide mentions switching on OEM. Can anyone help me?

Regain your privacy! Adopt /e/OS the deGoogled mobile OS and online servicesphone

oem unlock? basically

If you go through the “official (or community) install doc” for each of your devices at and click in the result page for the device on the “Command line” card with the “install” link it will walk you through.

Lots of text though