Previous versions licensed under LGPL will remain licensed as such. The current maintainers have no obligation to contribute distributing the older versions, but they aren’t permitted to prevent others from distributing it or modifying or doing anything else that was permitted by the license.
And, yes, to change from GPL/LGPL to another license you would need all of the contributors to consent, or to rewrite the parts that were contributed by anyone who doesn’t agree with the license change. Since it looks like there only one contributor according to the GitHub page, this probably wasn’t too difficult.
Here’s the direct link: https://foundation.mozilla.org/en/campaigns/whatsapp-must-act-to-protect-elections/