3 wire cooktop, 4 wire stove, 4 wire supply - what to do about neutral and ground?
In this case, you connect like to like.

The cooktop does not have a neutral (white) wire.

This is perfectly fine. The cooktop has no 120Volt loads, so it does not NEED a white wire.

[ The concerning case is when an old device has black, red, &amp; white, but no ground (green or bare) ]