Where does it say that? Here is exactly the page I see: https://web.archive.org/web/20240912104240/https://docs.hetz...

> Plans (CCX) with dedicated vCPUs have their CPU resources exclusively. Here one vCPU equals one thread of a physical CPU core. Instances with dedicated vCPUs offer continuous and predictable high CPU performance. We recommend them for systems with high production loads and CPU intensive applications. They run on high-performance hardware and come with a generous allocation of I/O and network power.

Of course that implies there is some throttling. But I see nothing about a hard 20% cap.