When I run
xrandr --newmode "2560x1440_60.00" 241.70 2560 2608 2640 2720 1440 1443 1448 1481 +hsync +vsync
and then
xrandr --addmode HDMI-1 2560x1440_60
I get
xrandr: cannot find mode "2560x1440_60"
For quite a few posts you're getting the "cannot find mode "2560x1440_60"" because it doesn’t exist, "2560x1440_60.00" does! You left off the ".00"
So the command
xrandr --addmode HDMI-1 2560x1440_60
should have been
xrandr --addmode HDMI-1 2560x1440_60.00