Is this an guide official?

No, but there currently isn't an official guide, and I am working in collaboration with the creator of xovi (asivery).

Can xovi brick my tablet?

Short answer: no (if you follow the instructions)

Longer answer: xovi does not touch your / partition (only temporary), so even if you made a mistake during the installation, xovi will crash, and its config in /etc/systemd/system/xochitl.service.d/xovi.conf will be unmounted, causing the device to reboot to the original OS. This means that the only way your device gets bricked is if you try to do something on your own, without the knowledge/understanding.

Where to get support?

If you need help, you can open a #support thread in the reMarkable community discord
For official support (not xovi related) go to support.remarkable.com

Why are there no extensions for beta?

When installing beta, you have to agree to the EULA for Opt-In Beta. The "Program eligibility" section states:

Due to the risky nature of Software development, You may not have any third party software installed on your reMarkable paper tablet while participating in this Program.

So installing third-party software like xovi and extensions for it is not allowed, which is why most developers don't make versions of their extensions for beta.

Software version

Go to Settings > General > Software

Supported versions: 3.15+
Recommended version: 3.22 (most supported)

If you have other third-party software installed on an older version (e.g. Toltec), make sure to back up its data and uninstall it before updating. If your version is below 3.11, the update will be done in 2 parts, first to 3.11, and then to latest.

Starting xovi

To make sure xovi works, and see debug output:

xovi/debug

To start/restart xovi (only if debug did not crash):

xovi/start

If it crashed, please try following the instructions again or see where to get support

To stop xovi and start the default OS:

xovi/stock

By default, you will have to start xovi after every restart. Installing tripletap is recommended, as it allows you to start xovi by triple-pressing the power button.