Yes, in principle teleconverters multiply focal length when stacked, so two 2x converters would act like 4x, and a 1.4x plus 2x would give 2.8x. The maximum aperture is reduced by the same factors, so you lose a lot of light.

The main issue is compatibility. Canon’s own EF teleconverters generally are not designed to stack physically because their front element/shroud protrudes, and the rear of another teleconverter usually won’t accept it. Third-party converters may stack more easily, but operation may become limited and manual control/focus may be necessary.

The bigger practical drawback is image quality. Each teleconverter magnifies not only the image but also lens aberrations, softness, and contrast loss, so stacking two typically causes a significant drop in sharpness and overall quality. Autofocus performance also suffers as the effective aperture gets smaller; AF is generally much happier at brighter effective apertures and may become unreliable or unavailable as you stack converters.

So: possible with some hardware combinations, but usually not advisable unless you accept major losses in light, AF performance, and image quality.