A good article which covers a lot of aspects, including what happened technically, which software flaws were exploited, that the problem affected refrigerators which did not have updated firmware. It also mentions the EU cyber resiliency act, which has the specific goal to avoid such events.

Making industrial systems secure will be many years of work, since many are decades old and software and protocols were not designed with security in mind. This also affects consumer "smart home" systems and things like "smart TVs", which are often not designed to have needed updates.

Worth mentioning that the effects of systematic attacks could be far worse - they can take out electricity, energy, and water infrastructure, payment systems, and bring things like chemical plants into an catastrophically unsafe state. The thriller "Blackout - Tomorrow will be too late" by Marc Elsberg describes such a (fictional) scenario with hacks targeting smart meters and industrial control systems for power plants, and it is in parts more realistic than one would wish. IIRC there have been such hacks targeting the oil company Saudi Aramco.