I want to provide a quick update for this topic. this feature, Ability to vote on an issue, is being under consideration to be built Jira cloud. we will keep you posted with the updates. I know this has taken a while to build out, but rebuilding Jira issues is no small feat, so we very much appreciate your patience on this.
In the meantime, try to utilize a custom field or you can opt out of this new issue experience via your Personal Settings > Jira Labs section will have a 'new issue view' toggle to turn it on or off. We will not be disabling this opt-out option until we have rebuilt all the key features of the Jira issues experience you have come to know and love.