I have tried this on a clean install of magento 2.4.1

I then went to a magento 2.3.6 ran grunt exec and grunt less both worked
After upgrading the 2.3.6 to 2.4.1 the grunt exec then failed with the same error as the clean 2.4.1

Im running MAMP Pro on mac os

Running "exec:blank" (exec) task
Running "clean:blank" (clean) task
>> 405 paths cleaned.

Done.


Execution Time (2021-02-05 16:40:48 UTC-0)
loading tasks   49ms  ▇▇▇▇▇▇▇▇▇▇▇ 22%
clean:blank    167ms  ▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇ 77%
Total 218ms

>> Exited with code: 255.
>> Error executing child process: Error: Process exited with code 255.
Warning: Task "exec:blank" failed. Use --force to continue.

Aborted due to warnings.


Execution Time (2021-02-05 16:40:47 UTC-0)
loading tasks  82ms  ▇▇▇▇ 7%
exec:blank     1.1s  ▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇ 93%
Total 1.2s