Hello @Nanook78, welcome to the community!
I do understand that it's frustrating, but the option to clear all cache with one click is removed in Android 8, due to a decision made by Google.
You can still clear cache in the apps by going to Settings > Apps and notifications > App Info, and find the app you want to clear cache in. Tap the app and choose Storage. Here you have the option to clear cache.
You can also have a look in the Google Play store and see if there are any applications that you can download that will clear the cache for all your applications at once.
I hope you have a nice day!
