i am not sure what is otrs user. i think it is not relaTED to OTRS Daemon because this serivce should not running in the beginning as in OTRS Installation Doc so i am not sure if i should look in this part. regarding to the system i created user called otrs then i created also one group called otrs user but still the same error so i i think it is not under system .
On windows server 2012 R2 i did not find WSL.
I installed Active v 5.16 without PerlEx. it is one feature make otrs very quick more than perl.exe. i am using now perl.exe to run otrs.
OTRS said you should use PerlEx to make otrs faster. PerlEx is expensive 999 $ pro year.