Two different ways to open a project in IDE's for MCUs
IAR is a proprietary IDE solution, where CCS and STM32CubeIDE buth use the open source project Eclipse as foundation.
IAR uses project files, Eclipse uses workspace folders.
Two completely different approaches with each their advantages or disadvantages.
One of which is that you can't double-click on a folder and open it in a program.

Perhaps there is some shortcut/bash file you can use that calls up the IDE with arguments to open some workspace