Please check:

• CPU quotas, please request to increase them anyway https://go.aws/3EvY1fX and use pools to have better control as old instances can be there for a moment after termination,
• Check the network configuration. Maybe it is downloading something from the internet, and the network is blocked/slow, especially third-part libraries can cause the problem.
• Start a new cluster with default databricks config. When it works, please add libraries step by step.
• Please check driver logs - there can be more details.