After a quick google search regarding this issue, it seems that there is no clear “solution” around.

The problem:
On a high dpi screen, the UI is extremely big, or extremely small depending on your current resolution or multiple screens.

However, as substance is based on qt, is easy to scale the UI with an environment variable
In linux (not tested in Windows, but should work as well), run this before opening Substance Painter (Substance Designer does have the option inside the application):

Do not add this to your system environment as it will affect other QT apps!

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