The linked article is an alarmist piece about the alleged risks of renewables and does not quote any reliable sources. I couldn't find any independent claim that anything unusual or alarming happened on August 14. Load shedding is a normal procedure and almost certainly didn't cause "a lot of damage" - it's industrial customers buying electricity at a discount in exchange for disconnecting from the grid when needed. This is only done for industrial processes that can be safely interrupted (like aluminium processing plants).
If anything, it shows that the mechanism works as intended. There wasn't any notable frequency deviation on Aug 14 in the European grid. All the graphs look normal - there was a ~15 GW deficit in Germany which was compensated[4], well within normal operating parameters.
In spite of the increasing complexity of managing the power grid due to renewables (a real problem which requires significant investments to solve), the German power grid is more reliable than ever[5].
[1]: https://eike-klima-energie.eu/die-mission/grundsatzpapier-kl...
[2]: https://de.wikipedia.org/wiki/Europ%C3%A4isches_Institut_f%C...
[3]: https://www.quarks.de/podcast/quarks-science-cops-der-fall-e...
[4]: https://energy-charts.info/charts/power/chart.htm?l=de&c=DE&...
[5]: https://app.handelsblatt.com/unternehmen/energie/energiewirt...