You are the first one to report this, but checking this on my PC, I indeed have 100% GPU usage as well on a 1080. The game runs smoothly though and my fans are not as loud as you describe. I can't check the Unity project right now as I have it archived on another external harddrive, but after doing a quick google search I assume it's a Unity issue from that older engine version I used to make this game back in 2017.
One thing I can assure you 100% is that there are no bitcoin miners in or anywhere near this game ;)
But thanks for bringing up the issue!