I have a Macbook 14" ( M1 Pro ) with 16GB of RAM.
However, the Force Quit Applications window pops up when I surpass the ~10GB of RAM utilization.
Even if I close some applications, this window keeps popping up after a short while. The system becomes unusable until I restart it. This mostly happens after 16-20h of uptime.
Attached is the picture of htop output and the popup. I did not close any applications; I just waited for the popup to appear.