Could you provide more details on the usecase that conduct to this 404 error?
Note that this site is not supposed to display something with a web browser, I also get a 404 error in Chrome even if update-site works like a charm through STM32CubeIDE.
What happen if you press the reload button of STM32CubeIDE repository site?
To give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.