M43, when it was introduced in 2008, was one of the earlier mirrorless mounts. It offered significant size/weight savings over its contemporary DSLR counterparts due to a combination of being mirrorless (much shorter distance between the lens flange and the actual sensor) and the fact that a physically smaller sensor doesn’t need such a large image circle. Mirrorless cameras have largely caught up in terms of flange distance, but the smaller sensor size means that for a given equivalent focal length and non-equivalent f-stop a M43 lens will be quite a bit smaller and lighter than a lens for another format. This does start to go out the window when you consider that a M43 sensor is about 1 2/3 stops behind a FF sensor in terms of noise until you get to longer focal lengths and M43 becomes king again. There’s a reason why M43 is so popular among birders.

If you’re interested in picking up a camera for macro photography, or another photography topic in general, I suggest heading over to !photography@lemmy.world and/or !photography@lemmy.ml. (Or the DPReview forums). Ultimately, camera recommendations come down to budget and what you will be taking photos of since that will guide AF/low light/macro/reach/etc needs.