Did you try to modify or add the software sites (repository) in CubeIDE?
If you did, please go to Window > Preferences > Install/Update > Available Software Sites . Edit STM32CubeIDE Releases and set location at http://sw-center.st.com/stm32cubeide/updatesite1
PS: This forum is intended for System Workbench for STM32, System Workbench is normally not supposed to run on CubeIDE. You might find more relevant answer on ST forums.