Are this information is actual now time?
Comment this please, This information can confuse people, (the first answer in a search engine on question about limitation of key requests)
Is there a limit to the number of requests marked as key requests?
If someone search this on Internet the 2021 updated info is the following:
Dynatrace allows you to create a maximum of 500 key user actions per environment across all applications and a maximum of 100 key user actions per application. When you reach that limit, consider using calculated metrics for Real User Monitoring, which offer similar capabilities.
You can check this here https://www.dynatrace.com/support/help/shortlink/user-actions#key-user-actions