We've published experimental releases of GrapheneOS for the Pixel 6a with full support for the hardware. Our web installer has also been extended with support for the Pixel 6a. There are currently no known issues with the release that's currently in all 3 release channels (Stable, Beta and Alpha) for the Pixel 6a. However, it hasn't been tested much and there are likely still issues that need to be reported to us and resolved. The best place to report issues at this point is in the #testing:grapheneos.org chat room on Matrix rather than the issue tracker. Issues can be opened once they're discussed there if there isn't a quick fix.
OEM unlocking toggle in the stock OS is currently buggy and we've provided instructions on how to work around the issue in both the CLI and web installation guides. This currently makes installation much less convenient, especially for web installation. It will be much better once the stock OS has an over-the-air update available for most users. At the moment, the update is gated as only being available to users on Japanese carriers or Verizon. The workaround for the issue is updating to the newer stock OS release and then doing a factory reset. We've confirmed that this works on the generic OS release currently gated as a Verizon only release. It's likely only available to Verizon users due to not yet going through the standard 4 weeks of testing and Google's close relationship with Verizon for Pixels likely allowed them to ship it early, although the details aren't known.