I installed the experimental build a few weeks ago onto my Pixel 10 Pro XL. I'm on the Stable channel, build number 2025121701. I haven't made any major modifications to the phone nor any call related permissions.
One issue has emerged. I'm unable to receive calls now. This hasn't been the case the entire period, just noticed it today. It is possible the issue has been here for a week or so, I'm not exactly sure when I last received a call. I can make outgoing calls just fine. I'm not sure if this is related to GrapheneOS or not but it seems worth mentioning.
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Ironically, as I was typing this, I was prompted for a system update. This updated me to 2025122501. This appears to have fixed the issue with receiving calls. I'm leaving this here as an FYI for anyone who encounters a similar issue.