That warning is a reminder to me that I own the device and can do whatever the fuck I want with it.

Doubtful.

LG did the same thing and I want to say it was a requirement of Google's to do so if they wanted to install the G-Apps on the system by the manufacturer.

Relock the bootloader.

Cannot be done afaik, it's part of the 'bios' self-check

Unfortunately, no. I'm running LineageOS on a Motorola device and the support docs state that there's nothing that can be done about this once its unlocked.

Depending on the device, unlocking the bootloader may have "blown" a "soft fuse". No idea if that's the case with yours. I assume you unlocked it to flash a custom ROM or similar. On previous occasions I've been able to re-lock a bootloader when I was running a signed rom and recovery, but I've neither unlocked or flashed a phone in years. YMMV, but re-locking would be the only way I know to remove the warning.