Why can't I enable sticky keys on my Macbook Pro?

Help! I broke my arm and need to enable sticky keys to work, but in the accessibility settings it is grayed-out (see screenshots below). I can enable every other accessibility functionality other than this. I've tried restarting and hitting shift 5 times. I've been able to create custom buttons in the onscreen keyboard that have the option to be "sticky", but instead of being like the key is held down, it's more like it's being hit repeatedly at my keyboard's repeat rate, which is not helpful. My laptop is a 16-inch, 2019 macbook pro, running MacOS 15.3.2. **Update:** I followed @LincDavis's terminal instructions in the answer below. Here is the output: ~ % defaults write com.apple.universalaccess stickyKey -bool TRUE 2025-04-07 11:53:59.331 defaults[4064:432848] Could not write domain com.apple.universalaccess; exiting ~ % defaults read com.apple.universalaccess stickyKey 0 ~ % plutil -lint ~/Library/Preferences/com.apple.universalaccess.plist /Users/myUserName/Library/Preferences/com.apple.universalaccess.plist: OK