Hi Audrey Jeane,
could you please confirm the version of Lightroom that you are using?
Check if your version is upto date.
Also, would suggest you to try the following steps :
1. Quit Lightroom
2. Open Adobe Creative Cloud application
3. click on gear icon on top right> Preferences> sign out
4. Sign in back to the Creative Cloud application
5. Launch Lightroom and see if you are able to turn on the syncing.
I have the newest version.
I will try those steps and let you know!