The graphics look plastic. Is it not because of an engine? Serious question.

I would say yes and no. Yes, obviously the renderer is there but at the same time it's only doing what it was told to do. Taking Unity and Unreal as examples, you can make something look plastic, cartoony, realistic, a mixture, or really anything you want. Usually there will be art director(s) (or a someone with a similar title) that make sure the art/graphics stick with a certain look and feel so I would put the blame more on them than the engine.

I don't know of any engines that dictate material properties. There are some where the default settings on the default materials are questionable coughUnity3Dcough. But a big studio game shouldn't/wouldn't be using the defaults on just about anything.

One of the biggest things indie game developers can do to not look like an indie game is to stop using the default settings on the default materials. Not necessarily even using custom materials. Just don't use the default settings.

It's hard to know for sure but most people believe they did a ton of either super rushed manual work and/or AI upscaling on the textures and models that would explain the "plastic" look to everything. It doesn't really matter what engine is backing it if the textures and modeling are bad. And if they didn't spend the time to sort out material properties then the engine won't treat skin any differently than cloth, or cloth differently than metal, etc.

these are more examples of modelling issues but it shows how little care and QA went into the remake:

they rounded out this 6-sided nut : https://old.reddit.com/r/GTA/comments/quutz7/definitive_lazy...

hot dog fingers: https://www.youtube.com/watch?v=qQWw0hHMUoc

Of course not. Unreal Engine uses a PBR pipeline as any modern engine does. If your materials look plastic it's because that how you authored them, not because of the engine.