DM here. I’m going to call this as a soft “yes”, but it’s gonna call for house rules.

Reanimation and necromancy in general, involves some enchantment of bits and pieces that had some mechanical basis in a living being. So we get the skeleton-zombie spectrum of reanimated remains. But break it down any further than that, and it becomes quite impossible - you don’t see choking bone dust clouds or jaw-less skulls rolling about the dungeon. But I would say that the distinction between enchantment and necromancy is the basic stuff of the object’s construction.

That said, one can enchant most anything with enough magic. So any inanimate object, even crude oil, could feasibly be turned into some kind of golem. That includes OP’s jello-mold-as-gelatinous-cube monster. The plastic parts idea is inspired - a monster that is spawned from a city’s midden (trash heap) would be truly dreadful and a sight to behold.

Also, there’s this:

Re-animated jello molds

I always assumed slimes were some sort of advanced slime mold. They get relatively bigger, but have all the same colors, and both are kinda all over the place.

Pictures because slime mold is freakin awesome.

Too late, she’s decided to invite her father in law for desert