My reboots are happening while using Xcode previews, that is a known issue :) From the release notes of Xcode 26 Beta 4: Xcode Previews usage will frequently panic on macOS 26.0 Tahoe beta 4. (141641869) Checkout this thread: https://developer.apple.com/forums/thread/794221

Same problems here. I've had multiple reboots in just the last hour.