Hey. Just saw this, and am on a Google pixel with pie, and have no problem tethering, as I discovered a homerun of a fix, provided you have root.
Just download VPN hotspot (by mygod), VPN tether (by jarvanh) and a VPN (I use the one with the bears in the tunnel). Turn the VPN on, then enter VPN hotspot. Toggle hotspot IN THE APP ONLY, return and enable the wlan0 option that will appear after hotspot engages. Then, open VPN tether, toggle on, and Viola! Endless hotspot. It will be viewable on your data usage only under the app title of your VPN, and thus as unlimited as any other usage.
As with all things, however, there's a drawback, which is excessive battery drain. But it definitely works and can be done, for free, and without a build prop tweak, as I haven't bothered working it in anymore, because I am positive it doesn't matter. But, if you wanted to stick with the prop tweak, add it to your /default.prop as well as /system/build.prop and then in a terminal (as root) enter "setprop net.tethering.noprovisioning true"
Which can be verified with the command "getprop net.tethering.noprovisioning".
Hopefully you enjoy.