@Mr_NutterButter i'm assuming you already made sure your RAM is all being registered in the OS. maybe one stick got unseated somehow or just died? make sure that your memory is all slotted correctly to make use of dual channel as well. if you don't have 2 or more sticks of RAM then you should, 2 sticks of 8gb is a lot better than 1 stick of 16gb.

check how your GPU/CPU temps are doing while gaming too. if they're getting too hot and throttling there's a chance that it could negatively affect your performance and you're seeing that as an increase in RAM usage and it is becoming a "bottleneck." i can see this definitely being the problem if you're on a laptop or using integrated graphics on a CPU.

you could also try turning on vsync or limiting the frame rate and see how the percentage of RAM being used is affected.

i do know that running some games unlocked will give you stutters because the frame rate will be really inconsistent, so it might be worth trying to lock down to your monitor's refresh rate just to see what happens.

then it could also potentially be something like nvidia geforce experience running automatically when you start a game, or some weird sort of other piece of software booting up alongside the game eating a bunch of memory too. when you launch a game, just try to have that task manager open to see if it really is the game that's eating your RAM or if there is something else. even if it isn't the something else, maybe it is hooking into the game and causing the game to eat more memory.