Invalid IMPORT operator for udev rules
Commits 8040f946 and 19898eb2 make udevd unhappy:
[12323.655258] systemd-udevd[8111]: /lib/udev/rules.d/80-libinput-device-groups.rules:4 IMPORT key takes '==' or '!=' operator, assuming '==', but please fix it.
[12323.655773] systemd-udevd[8111]: /lib/udev/rules.d/90-libinput-fuzz-override.rules:20 IMPORT key takes '==' or '!=' operator, assuming '==', but please fix it.
[12323.655783] systemd-udevd[8111]: /lib/udev/rules.d/90-libinput-fuzz-override.rules:25 IMPORT key takes '==' or '!=' operator, assuming '==', but please fix it.
So I suppose you need a different approach to fix the issue you tried to fix with the +=
operator.
This was initially reported downstream at Gentoo: https://bugs.gentoo.org/714876