This is definitely not true. GrapheneOS is focused on privacy, security, and usability. It has many features that are solely for increasing privacy and control and implemented in very robust ways. For a couple of examples, see the Contacts and Storage Scopes features.

This is a common misconception people have as a result of misinformation being spread.

They have officially stated that they can support the 10 now, but it will have to wait until after the port to QPR1. https://xcancel.com/GrapheneOS/status/1960792610114511190#m

That device didn’t meet the requirements for GrapheneOS even when it was supported by the OEM. As of now, it is an EOL device and is highly insecure. https://grapheneos.org/faq#future-devices

LineageOS also significantly regresses security compared to barebones AOSP.

• Userdebug builds
• No locked bootloader or verified boot
• Incomplete backports of patches