Respectfully, this is not true anymore. GrapheneOS works like a charm for most that use it. There are some issues regarding push notifications (if you decide not to install Google Play Services on your phone), but other than that the phones retain their usual functionality.

Additionally, the part of your comment regarding running old insecure kernels is not at all the case for GrapheneOS. The whole point with the OS is to run the latest security updates/patches and kernel. Take a look at the part on their website regarding patches for more information: https://grapheneos.org/features#more-complete-patching