Ensure your GPU drivers are up to date. KiCad’s "Accelerated Canvas" uses OpenGL, which can be buggy on the default "Generic" Windows 7 drivers. Can you run KiCad 6 or 7 on Windows 7?
Most Windows 7 machines are 64-bit; look for the x86_64 installer (approx. 1.2 GB). Kicad For Windows 7
Massive library of tutorials and forum posts specifically for the 5.1 interface. Ensure your GPU drivers are up to date
Version 5.1.x was built specifically with Windows 7, 8.1, and 10 in mind. Kicad For Windows 7
Right-click the installer and select "Run as Administrator" to ensure it has the permissions to register system DLLs.
Completely free with no subscription or "lite" version limitations.
You can find these older installers in the KiCad Windows Repository . How to Install KiCad on Windows 7