Again, it's a rumor, but it IS published in the Taiwanese newspaper Digitimes (translation below), it does carry more weight than a social media post. It also would mean that, as it is a 2021 product, AMD would be under no obligation whatsoever to 300 series motherboards to support them. It is also EXACTLY what every other company has done when there is a lack of competition: sit back and collect money from old products while holding new ones from sale.
https://wccftech.com/amd-allegedly-delaying-ryzen-4000-series-zen-3-cpus-to-2021/