Yeah I had a feeling, so I looked it up and turns out it's because of RPGMaker, not really the game itself
Yes, you are right. By default, RPG Maker MV games use a "sort" of monitor synch included into the game engine core.
Which is generally a problem when using a monitor/screen using a low refresh rate (with some devices on android, for instance). It's rarely the inverse (I mean with a very high refresh rate): but apparently, it also sometimes happens.
There is a plugin to fix this (once again generally when using a low refresh rate): the "FPS Synch Option" plugin (part of YEP, i.e. Yanfly Engine Plugins).
Some games incorporate it, and in this case there is usually an "FPS Synch" entry in the main options of the game. But this is not mandatory, which means that not all the RPGM MV games have it.