The first one was built in 2021 and went into commercial operation in 2023: https://www.ans.org/news/article-6241/china-pebblebed-reacto...
It was conceptualized in the 50s: https://en.wikipedia.org/wiki/Pebble-bed_reactor
But there were a number of limiting factors that led to people building reactors that could meltdown, but were incredibly unlikely - see Fukushima - it didn't technically meltdown - even in a VERY bad scenario with a good bit of human error.
They don't need fanatical attention to active cooling, but they do instead need fanatical control of the atmosphere near the reactor to prevent fires, for example.
The first prototype was built in Germany in the 60s. It was closed in 1988, had to be bailed out by the German government in 2003 and has of course been a continuous money drain on German taxpayers ever since.
Nice summary here: https://en.wikipedia.org/wiki/AVR_reactor
From basic principles one might consider that anything that generates enormous amounts of power in a concentrated area can never be truly safe. All that energy is always a potential disaster.
Power plants that generate less power but are cheaper to make and can be distributed over a large area to ensure redundancy is a better strategy for both safety and reliability.
Meltdowns are also not the only risk. That Wikipedia article says the PBR concept was used in the AVR reactor and still resulted in a non-meltdown accident that contaminated the groundwater with radioactive substances. Again they couldn't attribute deaths to it, but the main article https://en.wikipedia.org/wiki/AVR_reactor makes it look like an expensive mess with many accidents and protocol breaches. 1966 though; hopefully they've learned.