XPS 15 Resolution blurry and incorrectly scaled

I'm going to guess you have the 4K display?  If so, Windows would have enable display scaling because 4K resolution on a 15" display would be completely unusable at standard scale factors.  The default scale factor would be 200%, I believe, although you can adjust that in Windows Display Settings.  As for what you can do, probably nothing.  Scaling support within Windows is still very inconsistent for a variety of reasons.  Even portions of Windows itself still don't scale nicely, although it's been getting better over successive releases of Windows 10.  But basically, Windows has introduced several different scaling mechanisms over the years, and it's up to application developers to implement support for them.  Some support the latest and greatest, some only support legacy scaling algorithms, and some don't scale at all.  And then Windows gives users options to try to force scaling on some apps -- so like I said, you can end up with very inconsistent results from app to app.

The only thing you CAN control is to make sure that your primary display doesn't change within your Windows session.  Windows selects the display scale factor to use for internal rendering based on the scale factor of the display that was primary at the time the user logged in, and if the scale factor of the primary display changes mid-session, it essentially shrinks or blows up the output post-rendering to compensate, which definitely looks bad.  So for example let's say you log onto your PC when you only have your 4K 15" display active.  Windows will be rendering at 200%.  Then let's say you connect a 24" 1080p external display, which would use a scale factor of 100%.  That display won't look as good as it would when used on its own, because Windows will still be rendering internally at 200% and then shrinking the output that gets sent to that display, which introduces blurriness compared to actually rendering at 100% internally.  Even if you set that external display as primary in the middle of your user session, the internal rendering won't change until you log off and back on.  By the same token, if you logged on while you had that external display connected and set as primary, then your 4K panel wouldn't look as good as it could, even if you disconnected the external display and started using only the 4K panel -- until you logged off and back on.

As you can see, scaling is still a bit of a mess in Windows.  That's especially true if you ever try to use multiple displays with different scale factors simultaneously, but even if you're only trying to use a single scale factor, if it's something other than 100%, some things simply won't look right.  Again, even some portions of Windows and some of Microsoft's own applications don't scale cleanly.