I’m in the exact same situation, however the right shift key broke, and activates randomly. This laptop only ever moved between a cupboard and a desk, without the tiniest bump, but after a couple months of very light use the shift key breaks. I now have to have sticky keys enabled permanently.
Also the only way to enable sticky keys on the login screen is to triple click the power button. You would thing they could just put a button for the accessibility accessibility menu next to the one for the keyboard layout switcher, but no.