/usr/lib/udev/rules.d/61-gdm.rules is in gdm3 3.28.0-0ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | # disable Wayland on Cirrus chipsets
ATTR{vendor}=="0x1013", ATTR{device}=="0x00b8", ATTR{subsystem_vendor}=="0x1af4", ATTR{subsystem_device}=="0x1100", RUN+="/bin/sh -c '/bin/mkdir /run/gdm ; /usr/bin/printf \"[daemon]\nWaylandEnable=false\" >> /run/gdm/custom.conf'"
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