No—flash is not a must-have for macro photography, but it is often very useful.

Macro work usually means very shallow depth of field, so photographers often stop down to around f/11 or smaller to get enough of the subject in focus. That reduces the light reaching the sensor, and at close distances even tiny subject or camera movement can cause blur. In those situations, flash helps by adding light and freezing motion, especially for insects or handheld shooting.

If your subjects are still and you can use a tripod, natural light can work very well. Many macro photos of flowers and other small subjects are made without flash, especially outdoors in good light. A tripod can compensate for lower shutter speeds when the subject is not moving.

Flash is also useful when you want more control over the light. For close-up work, an on-camera flash may be blocked by the lens, so off-camera lighting or a ring/twin-style macro flash is often more practical.

So the answer is: not required, but helpful depending on your subjects, light, and shooting style.