Pixel 4 OEM unlock impossible?

My new Pixel 4 just arrived, and I want to install LineageOS on it. Problem is, the OEM Unlock toggle is disabled (greyed out). It's not a carrier-locked device or anything like that (purchased from a Dutch retailer). I've tried a bunch of "fixes", mostly various combinations of factory reset, with and without WiFi or SIM, the adb shell pm uninstall --user 0 com.android.phone command, etc. Are there any other options, like sideloading a custom recovery (if that's even possible)? Or is there a chance it will become available after 7 days as I've read somewhere?