Can you share which version of Tableau Desktop you are using? We upgraded and changed quite a few code modules to address 4K monitors last year. Is this Windows 10? Latest version of Windows? HDMI? Just trying to determine what your setup is. I use a 4K monitor but on a Mac and have never had an issue but I think that is due to operating system differences.
Could be due to OS difference....
I am using Windows 10 Home Ver 1903.
Tableuau Ver is 2020.1
I wonder if you tried all these options: https://kb.tableau.com/articles/issue/overriding-display-scaling-on-high-dpi-monitors
I'm still researching as I heard about this a couple years ago and we fixed something related to this on Windows versions.