This might not cover everything but is what I know to get the cable link to work.
First you need to enable developer mode on your meta horizon app.
1. Go to meta horizon --> Menu in upper left. --> Devices, first option on the top then add your headset or connect if needed. --> Headset settings. --> Developer mode. --> make sure it is switched on, the switch will be green if on.
PRN. If you need to verify, login into developer.meta.com , click your profile in the upper right, then click my projects, to do the verification add 2FA or a credit card, then name your "Team" whatever you want, this part dosen't matter, after doing this you can go back to meta horizon app and repeat those steps.
note : This what i had to do at the time, I'm looking at developer.meta.com and it looks different to what i remember.
2. Restart your headset, then connect your cable, you'll get a prompt to "Allow USB debugging" click always allow from this computer, then go to your settings --> link, then scroll down and at the bottom turn on "USB connection for apps."
Note : From what I've tested enabling the beta on quest, steam VR, and the steam app is not needed.
3. Make sure your cable connection connecting your PC and headset is good, then go into the steam VR app in your Q3, you should see a USB-C icon in the upper right, connect to your pc then go to Steam in the bottom left --> VR settings. --> Steam link, scroll all the way down, and make sure "Allow multiple links" is on, this is the most important part, after that, look at your pc on steam VR, it should show a USB + WIFI connection, you can then turn off your wifi on your quest, disabling Metas ability to steal your data and a connection through just your cable.
Note : From what I've tested multi link is required because steam VR needs to make a UsbNcm that allows you to stream data via your cable, currently there isn't any way to use it without multi link but maybe some a feature will be added to connect through cable without wifi.
Let me know if there is anything I left out, I'll try to respond to questions but I probably don't know the answer to all of them.
Then again this is probably not a perfect tutorial but it's the process that I've done over the course of several months, allowing me to use a cable connection.
-HM2