We've retracted our recommendation to use fastboot from the android-tools package on Arch Linux. It's broken for flashing the Pixel 7 and Pixel 7 Pro.
We currently only recommend using the official platform-tools package or building fastboot from GrapheneOS or AOSP from source.
We've updated https://grapheneos.org/install/cli to remove that recommendation. Most users are installing GrapheneOS via our easy to use web installer at https://grapheneos.org/install/web instead where we provide the fastboot implementation via fastboot.js library created based on GrapheneOS funding.
It's unfortunate that seemingly every Linux distribution has broken Android SDK packages because they insist on checking out the sources their own way and using a custom build system instead of the official one. It's easy to build these tools properly if you do it normally.