That's how I feel about "performant". Unfortunately I'll never stop seeing such jargon every day or two, working in tech. It is what it is, I guess. :\
It means "of or pertaining to performance". Like "the performant qualities of this software are currently being evaluated", or the one example of its original meaning I could find from Cambridge Dictionary, "What follows is a series of re-mappings of both the performant and the referent functions that emphasizes the collective performance." The word itself doesn't indicate efficient/good performance, nor poor/slow/etc. ... It just refers to the quality or property of performance. For some reason, very recently it started being used to mean "performs well" or "performs optimally" and has transformed into jargon.