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.
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
bin/magento deploy static content methods work without error