Why do ICs interconnects have squared corners
Chamfered and beveled corners are used when the size of the interconnect is large relative to the wavelength of the signal, meaning that it begins to apply at microwave speeds at the PCB/microstrip scale.
IC interconnect is very small, such that it is small enough to not experience these effects strongly enough to need chamfered corners. Furthermore, very small IC interconnect hits the limits of manufacturing, with rectangular features often being drawn as small as possibly manufacturable--reliably chamfering those edges would be prohibitive.