Happened last night on Ubuntu 24.10 after disabling the same 3 BIOS settings (C-states, SpeedShift or the older one, HT); was fine several reboots earlier (all 3 on), toggled the settings, and immediate next boot had the locked X cursor. I was on Xorg so the headphone trick worked.
Even happened with auto-login, so now I’m not sure on any reliable way to stop this with GNOME. Probably over a hundred reboots with FreeBSD 14.2-R had no such issue (totally different env though rc.d startx Xfce), and this seems consistent on Fedora, Ubuntu, and openSUSE with GNOME, Xorg and Wayland.
I’m leaning heavily towards this being a GNOME-specific thing but don’t know if it could be something deeper like real-time or systemd. Windows and FreeBSD are consistently fine (making me also trust my hardware), and this wasn’t a problem prior to F38-F39.