When an app is pinned to the taskbar, its window does not automatically receive focus

Win+number is supposed to open the pinned app, or switch to it when it is already running, so the new window remaining unfocused is not the documented behavior. First determine whether this affects every pinned app or only one. If it is one app, unpin it, close all of its windows, pin it again, then go to Settings > Apps > Installed apps > the app’s Advanced options and select Repair if available; use Reset only if Repair fails because Reset can remove the app’s data. If all pinned apps are affected, install Windows updates and restart. Then test in a clean boot to rule out a startup software conflict. Re-enable disabled items in groups to identify the cause. If the problem persists in a clean boot, press Win+F immediately after reproducing it and submit a Feedback Hub report with the app names and whether Alt+Tab focuses them normally.