I think your studio is old version
Usually now it comes with 3 options
The Windows Legacy and cross platform option is designed to be compatible with serverless environments.
But it is important to note that the Windows Legacy option is deprecated and will be removed in future versions of UiPath Studio
Though currently, you can create new projects with the Windows - Legacy compatibility. In future Studio releases, you will only be able to open, edit, and run Windows - Legacy projects. However, organizations will still be able to use governance policies to restore the option of creating Windows – Legacy projects. The Windows - Legacy compatibility will only be deprecated once all official UiPath activity packages are available in Windows or cross-platform projects
choose accordingly to your need
If u see
Windows - Supports all platforms, including serverless environments.
Windows legacy - Supports only Windows-based serverless environments.
So better i would recommend to choose windows for now in your studio here that would still work in serverless and later change it to cross platform