You have different options that can happen when a queue is full. You can play a busy tone, Play voice message, send the call to a shared voicemail, or divert a call. Threshold in a queue.
All the Answer Groups has 20 callers as default
Click on the Answer Group you want to change the overflow on.
Click on Waiting Calls and then Call Overflow. You can change the default limit and change overflow handling.
You can choose between