Sure, Venezuela's military is a rolling circus, but the thing that has everyone worried is that Guyana... basically doesn't have a military at all. For example, they have no combat aviation and their entire air defense is a couple ancient MANPADS, while Venezuela has about 30 attack helicopter. They have no tanks, Venezuela has about a hundred T-72s, plus some other assorted armor. They have plenty of heavy artillery, Guyana has a couple of mortars. Etc.
There's also very little stopping le Putler from just supplying them with parts and giving them support, half of Venezuela's equipment is Soviet/Russian and he might do it just to troll Joepedo by starting another conflict, this time in basically his backyard.
Still, I'm expecting a shitshow where Maduro either eventually backs down and tries to pretend the referendum never happened, or possibly he starts the invasion and the Venezuelan army turns on each other before they engage any Guyana forces. Who knows.