There is no problem when it comes to CG, whereas the problem lies in the engine. RPG Maker VX runs on Ruby, while RPG Maker MV and MZ run on JavaScript. Why not just use VX with scaled CG? There is no way to increase the resolution in VX above 640x480. Period. There's nothing you can do about it, I've tried. Even if you increase the resolution, it wrecks a great many other things. Also, IMO VX sucks. So the problem lies in the coding language the engine was built on. For Clymenia games the issue is simple because he didn't use many plugins or script calls, but for games from OneOne1, changing the engine is virtually impossible unless you want to spend months on it.