Sending, receiving, and organizing email in Outlook.com
Hello
You will need to run the rules manually in this case, because otherwise the rules are for inbox only.
Go to https://www.outlook.com > Settings > Mails > Rules, click on the three dots of the rule and choose "run it now". It will ask you what folder to apply to, then you can pick Spam/Junk folder and it will run that way.
As for when or whether Msft will make this feature work automatically on Spam/Junk folder, unfortunately no one knows here since this is community forum. You are not talking to engineers or product people here.
In your outlook.com UI, go to Help, submit a feedback. Or do it here https://feedbackportal.microsoft.com/ That way your request will go to the right team. If there's any update, they typically would indicate via the Feedback platform.