Lightweight in software is a weird adjective. I used to assume it meant light on resources but after seeing what passes for "lightweight" I've disabused myself of that notion. Instead, I've seen it mean any of the following:

not-much-ceremony-to-use (e.g. https://github.com/emilk/loguru)

small amount of code but huge number of dependencies (e.g. micromodal https://github.com/ghosh/Micromodal/blob/master/yarn.lock )

But the common denominator appears to mean "feature incomplete".