I don't think it follows at all that social media is the cause. It's clearly an enabling factor, especially in places that didn't already have a healthy right wing media like the USA. The common cause is long-standing discontent over economic issues, unaddressed by liberal or center-left institutions, and a right wing eager to regain power by fomenting culture war.
There is long-standing discontent over economic issues, yet the people are equally furious about toxic 5G radio towers, and a thousand other delusions.
The public, before social media, was better informed about the world. They have access to much more information now, but that means little when the information they consume first has been sharted out the asshole of some idiot podcaster.
For various reasons, social media incentivizes knee-jerk antiestablishment takes: "Get angry! The MSM is hiding the horrible truth we are about to share with you! Like and subscribe or be kept under their control!" That is why any nation with social media, and a sufficient number of gullible citizens, tends towards violent revolution and pugilistic leadership.
Social media became a major force after 2010, and indiscriminately affects nations around the world.
Since the nations with rising authoritarian movements have little else in common, social media clearly is the cause.