I have same problem on some PC and windows 11 sandbox.
but working good my pc.
---- Edit -----
I Found the problem.
Since sometime the Syncfusion.SfInput.WPF.dll file is missing.
There seems to be a problem with dependencies.
I used version 19.4460.0.56,
However, after installing version Syncfusion WPF 22.1.34 Essential Studio a few days ago, I had this problem.
Added a reference to the SfDatePicker control to add the Syncfusion.SfInput.WPF.dll file to the output folder at build time.
Problem solved.