I've set up flows in power automate, so microsoft are 'kind of' made responsible for actually doing the spam removal work, even if I have had to set it up, https://make.powerautomate.com/ -> 'my flows' -> new flow -> call it 'spam block' or such, create a rule for outlook 'When a new email arrives (V2)' (to the junk folder, as only trusted emails should be going to inbox anyway)
Then add a condition (keep adding them as 'or' conditions) with condition 'from' - 'contains' - 'onmicrosoft.com' (you can choose any parts of an email, eg. 'body' or 'subject') then on the 'if' any of these or conditions (there's a limit of 10 per flow condition I've found) then do action 'delete email' (just goes to deleted items, as it would if manually deleted) and leave 'no' empty (email will just stay in junk if that's where it's gone).
Obviously, don't make the filters too wide ranging, try to be as specific as you can be to the junk email wording, or you might delete non junk in with them.