Why is the quality of the representation in the drawing window poor?
Why is the image slowly built up?
Why is no content displayed in the drawing window?

1)

Check whether the graphics support (hardware) is sufficient for a CAD application.

2)

Make sure that the graphics card driver is up to date.

3)

Gradually reduce the quality for rendering.

See Settings > Settings > general > Gruppe „Anzeige“

4)

If infra CONVERT is running in a virtual machine, pay special attention to the “Graphics” requirements in the system requirements.

See Installation > System requirements