Installing GrapheneOS on current Pixel 4a5g or buy a newer Pixel 7?

[GemStater]

You can unlock the developer options on any Android smartphone or tablet by locating the build number in your Settings menu and tapping it multiple times, normally 7 times. However, the exact location of the aforementioned build number may differ depending on your phone's manufacturer. Open settings and search Build.

Not so on some Pixels. Tapping the build number seven times will reveal the developer options are greyed out and not available...

Edit: To clarify, under developer options, it will be "OEM Unlocking" that is either available or greyed out, which is not available. I'll post a video of what to look for here: