Can the same user vote twice? What about guests?

I used the voting function.
At that time, the "join to voting." popup did not appear for users who had completed voting once. Is it correct to understand that the voting was successfully completed?
Also, in the case of guest participation, will a pop-up appear regardless of whether or not you have already voted?
I was worried whether I could vote properly, and I didn't know even if I looked it up, so I asked a question.
In addition, the voting period has already ended, and the editor cannot confirm the details of the results.