Nucleo f401 is supported and it should work out of the box with latest ac6 (cubemx 4.1+) that’s sure.
make sure to have stlink-v2 recent driver installed (what should be the case if ou have installed stm32-uitlity)
if you installed the toolset from st pakage re-installing or updating from eclipse using the site may help
With first earlier verison of CubeMX “board” was not set by defautl in ac6 c/c++ setting pane this making a null execption
f trying to create a debug config or launching debug, simply select a nucleo-f401re board should sollve the sisue
the same is lilkley to occur if you do not set the board in your c/c++ target ac6 setting.
Is the stm32f7 device and board cfg already supported by openocd shiped or insatlled with your ac6 plugin ?
Double check in the debug configuration and our the opencocd console (if possible) what’s the cfg file use in openocd
that file should exist on the opencd board/ or scripts subdir.