Maybe i've misunderstood which villain you were referring to in Solo? Who did you mean when you said "One moment towards the end left me rather confused about a certain villain making a little brief appearance because I don't remember seeing him in any of the other films"
Feel free to spoiler tag it
Ahh I see what you mean now!
I know the villain was Darth Maul who was the lower ranking baddie in Phantom Menace but I thought Obi Wan killed him and I don't remember him popping up in any of the Rey films so it seemed strange to have him have a rather pointless cameo at the end