Are joint slots only good for elemental materia?

I Got An Amazing Line Hit On 5 Elemental Slot Machine Which Was JACKPOT ! This Game Has

A child widget's slot is determined when the parent's updateChild method is called to inflate the child widget See RenderObjectElement for more details on

elemental gems megaways slot Elementals is a 5-reel Microgaming slot featuring sketches of fire, water, air and earth The slot includes wilds, scatters, free spins and a gamble mode

elemental slot I'm getting a bit confused about how to slot elemental mods to get the said combos, i understand the pairing but getting different opinions