What? Shutting down infrastructure, destroying critical records (economic collapse), spoofing / impersonating world leaders (confusion, panic, world war, nuclear event), taking over comms generally (you get a message to evacuate your home due to impending disaster, is it real?). All these could cause sufficient chaos and fear as to instigate global collapse. Once the panic sets in after a few of these indicidents, unrest and rebellion can occur, causing authoritarian backlashes or civil wars. IoT and precision ag can be controlled to disrupt supply chain and food supply. Forging documents to cause mass evictings, bankruptcy, credit disruption, transfer of property, asset seizure, arrests / SWAT-ing. Intelligence / signal gathering devices can be corrupted to spread misinfo and cause massive disruption or conflict. This is all possible today with enough hacking ability and malicious intent.

Anyone's life can be suddenly ruined: falsified criminal record, banks drained, credit cards maxed, phone numbers repossessed, internet, water, power shutoff. Friends and family sent your fabricated suicide note, warrants for your arrest issued to local and feds for kidnapping and threat to the president, etc. Injecting tons of copyrighted or illegal material into your hard drives, falsiying messages from your account and sending them publicly containing damning material. Sending messages to employees / employers to destroy business / work relationships. Harnessing your social media to destroy your life or cause panic. Getting you put onto pharmacy watch list so you can't access medications. Its very possible to ruin lives and destabilize the world without money or a physical body.

Now imagine this at scale and how it would affect the world at large if this was covertly done to a substantial portion of society and/or world leaders. Hell just shutting off all the "smart refrigerators" for a few days would cause a massive disruption to the first world.