empty731
Of you downloaded Play Store and the associated sandboxed Google Play services from the GOS app store I don't believe it's an issue. I haven't modified my Play Store settings and checked my other GOS device, it also is set to allow.
I'm not sure why yours is different. Only thing I can guess is you may have adjusted some settings that are applied globally so it's occurring there? Similar to all the exploit protection settings that can be individually adjusted but also globally.
If you're concerned, verify the boot hash on the start screen with what's on the GOS install page. That will confirm your device is running as it should be. You could delete the full sandboxed Google Play again, reboot, then install them again and check your install allowance.
But I'm fairly certain "allow" is what you'll want in Play Store, with "disallow" for files and any browsers you have. If you disallow there but get apps from trusted devs, you'll get a notice on screen to adjust this setting for download/updating. I do this for one of the apps I use directly from a developer, turning it on when I need then off once done.