Wikipedia currently treats them as synonyms (redirecting "retrowave" to synthwave) and I couldn't find any authoritative sources, but according to user Zsokorad on Reddit:
Synthwave is the all-encompassing genre of "music with synthesizer sounds". Synthwave started in the late 70s and has been around ever since to some degree. But there have been two ...
via reddit trapmetal , this documentary names a number of artists : for example Prxjek
Another compilation here, with names.
sounds as if the definition of "ragecore" is still fluid, or subject to some overlap with other similar genres.