If you have many pages/products it may cause an issue, that the cache is generating slowly.

To solve this, you can set the Prebuild Speed to Multithread, in that case prebuild will use multiple threads (you can limit threads in Optimization > General) to prebuild the cache.

Be careful!

Using multiple threads can lead server overload. It is recommended to use it only on VPS, dedicated or cloud server, where CPU time is not limited. It is recommended to use less threads than the number of CPU cores of your server.