Menus, tools and swatches are too big since 2019 update
It seems like it can't tell its on a 5k monitor?
See comparison below.
Illustrator 2019 compared to InDesign 2019
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Daniel Crabbe
shared this idea
Starting CC 2019 we are scaling the user interface a little on high resolution devices. To turn that off please use the small value as described on this page to get back the behaviour of previous release.
https://helpx.adobe.com/illustrator/using/customizing-workspace.html#Scaletheuserinterface