I've been suffering with really small icons in the toolbars with TCad ever since I started using high DPI monitors. I was talking with a engineer at Microsoft about this and they asked if I had set the system to override the application for High DPI screens. I you right click on the Tcad icon, and go to properties, under the "compatibility" tab select "Override high DPI scaling behavior, scaling performed by:" and set the System (Ehanced) as having control. This will apply the system scaling to the application (and in my case does a 2x on all of the pixels) which means that I don't get the benefit of a high dpi screen but at least it is usable for now. I expect this will continue to work until IMSI gets scaling done in the UI toolkit for the application.
TC Plat Pro 2018, Win 10, Surface Book, first TurboCAD version 3.0 (still have the disks)