Currently, GSI firmwares are developing very slowly, and their performance is envy from Vendora (Proprietary drivers). Not recommended for installation
FAQ onGoogle Apps (GApps) Always up-to-date versions of GApps packages onOpenGApps.org Following the link you need to choosePlatform : arm64, Android : 8.0/8.1/9.0, Variant : here any, depending on how many applications you need to be installed when you first start the OS, pico the smallest gapps, aroma the biggest, best bet stock .
In short, Pixel Experience 8.1 normal flight! Through TWRP it was stitched like a native. Immediately I can point out the already installed Gaps and Google Camera 2 api