Update: It IS possible to install Lineage OS GSI on the G8 Play. However, you will trigger a security error (nothing critical, since your phone will still boot up). To install it, you really need to flash the One Macro Firmware (evidently, your device can hard brick, but it's possible to fix it ). Later, you can flash the Lineage rom through fastboot.
Even though it's possible to install it and even boot it, the rom is buggy. It would be wonderful if anyone who knows better developing than me would work on this device, which has been abandoned for so long...
Some bugs of this rom are:
Fingerprint sensor sometimes triggers volume up or down.
The screen is not well adjusted, picture seems weird.
Dm-verity error which will not allow the phone to boot unless you press the power button again.
Bluetooth audio not working.
I have not tested the rom completely yet. However, I would like to get this forum revived again, with the possibility of "messing up" with the phone. It's not impossible, it just needs some attention