Oh damn thanks for the notifying me. I actually have a TV with a higher refresh rate connected to my PC, so I tried the game on it and it seems to run just fine. I've also never heard similar reports from anyone else, so it might have to do with your PC? Either way, I'll make sure to add a V-Sync toggle key to this and all my future games though, just in case.
Not sure how it would work if you have a TV or multiple displays connected, it might not support outputting over 60Hz to a TV (since I think TVs only go above 60hz for active 3D, many of the ones that advertise that they are 120 or 240hz actually only accept a 60hz signal and internally up-convert it to 120 or 240) or it might lock all the displays to a refresh rate that all of them can do.
Glad to hear about the V-Sync toggle being added. While obviously fixing the issue would be preferred, I admit that is harder to do (especially if you don't have a similar display to test) and could be a lot of work depending on how much of the game is tied to the refresh. If getting it to work with v-sync is too much of an issue, is it possible to somehow have the game detect if the display is above 60hz and default the v-sync to off if it is?
I used GameMaker: Studio for this so unfortunately what I can do to fix the issue is very limited, but I'm still pretty sure that the issue isn't just with higher refresh rate monitors since several others played the games I made with the same engine before. I'm pretty sure that at least one of them would also have a higher refresh rate monitor.
I even found a forum thread someone asking if that would happen and everyone's answer seems to be no: https://forum.yoyogames.com/index.php?threads/v-sync-question.40821