Currently, I am working as a SQL server developer from the last 4 years. What is the best technology now for my career growth?

You have multiple options

  1. Get more knowledge on SQLServer administration side including capacity planning, etc and move onto DBA space
  2. Get knowledge on BI related and cloud related tools like SSIS, Power BI, ADF etc and you can move to data platform space as a data engineer
  3. if you can add few other bits like Python, ML etc to your stack you can move to data science space and become data scientist

2 and 3 are new career paths which is quite active these days