Google supported devices list confirms your xdaforums link.
| Retail Branding | Marketing Name | Device | Model |
|---|---|---|---|
| “Razer” | “Razer Edge” | “Razer-Edge-WiFi” | “Razer Edge WiFi” |
| “Razer” | “Razer Edge 5G” | “RZ45-0460” | "Razer Edge 5G |
You did start from
Before following these instructions please ensure that the device is on the latest Android 12 firmware.
??
If yes … Try more permutations! 
Consider that the /e/OS dev is using
- a template which always unhelpfully starts “With the device powered off” … This means that the device should not be running, but does not include power down first.
- he added press Volume Down while plugging it into a PC,
- while he had the Lineage wiki in front of him.
So it implies simple following Lineage wiki didn’t work for him and he found he could add a extra trigger for success.
When I spent over a week to learn how to boot a Samsung into Custom recovery, I would not have described it as fiddling around. It was progressive repetition with slightly different style or timing each time.
Oh, and just in case you missed it, you have to flash recovery again after each failed attempt, as we have to assume the e-Recovery was wiped.