unable to write preferences in jetpack data store class not found exception
Answer #1 100 %I'm facing the same issue. The issue was because version 1.0.0-alpha03 missing datastore-preferences-proto library.
You can check the issue here.
Temporary solution for me is to use previous version 1.0.0-alpha02 while waiting until it got fixed.
UPDATE
The issue has been fixed in 1.0.0-alpha04.