I don’t get it. Unless the headline has been changed, there is nothing wrong with it as is. Clearly it says:
Parents not happy with CA student vaccine mandate PROTEST at Capitol.
The parents are not happy about the mandate and they are protesting it. How would you or anyone else here complaining about it reword it?
Protest could be a verb or a noun. This changes the meaning of the headline depending on how you use it. It’s poor English to so that.
It could mean parents not happy with the protest.
Parents not happy with
California student vaccine mandate protest at Capitol