What version and patch level of SAP GUI 7.X are you using?
See SAP Notes 2022335 and especially this one 2106323 - SAP GUI for Windows: DPI scaling of the Windows will be supported.
Starting with patch 3 of SAP GUI 7.40 the DPI settings of Windows will be taken into account. That means that e.g. with high resolution on a small screen and DPI settings greater than 100% SAP GUI for Windows will be shown as large as according to the DPI settings
Cheers,
Dan Mead