I recently attached a 1440p monitor to my PC and most applications (Reaper, Firefox, etc.) look great, but SF18 looks blurred. Is there any way to fix this?
Try using a High DPI override setting. Right-click the SFP <.exe> or the shortcut, Select 'Properties> Compatibility> Change high DPI settings' There are a few options so you may have experiment some..
In my case, the toolbar text and icons were to small to read on my 4k monitor (my old less than perfect eyes) so I adjusted high DPI settings. see screenshot.
Sadly, each new SF 'upgrade' introduces more new counter-productive issues (the redesigned batch tool for instance). I use SFP-14 or 15 more than SFP-18. For my usual work-flow, SFP-16 & 17 were mostly unusable due to the 32-bit VST-2 display issue. Personally I am disgusted.