Sending, receiving, and organizing email in Outlook.com
There is no information here indicating that Microsoft plans to restore the checkbox behavior permanently or on a specific timeline.
A currently documented workaround is to click the Select icon, shown as a box, at the right side of the folder name in the message list pane. That brings back the checkboxes for selecting messages.
If the concern is whether waiting 30 days will result in an announced fix, no such commitment is shown here.