kselftesttask: O= not working

For this task I'm supposed to upload a report.
But whenever I use O= to save my ouput on a specific location it throws error.

pegasus@pegasusv:/linux_work/linux_latest_bootable$ sudo make TARGETS="timers" O=/tmp/kselftest kselftest
[sudo] password for pegasus: 
make[1]: Entering directory '/tmp/kselftest'
  SYNC    include/config/auto.conf.cmd
***
*** The source tree is not clean, please run 'make mrproper'
*** in /linux_work/linux_latest_bootable
***
make[2]: *** [/linux_work/linux_latest_bootable/Makefile:646: outputmakefile] Error 1
/linux_work/linux_latest_bootable/Makefile:770: include/config/auto.conf.cmd: No such file or directory
make[1]: *** [/linux_work/linux_latest_bootable/Makefile:793: include/config/auto.conf.cmd] Error 2
make[1]: Leaving directory '/tmp/kselftest'
make: *** [Makefile:226: __sub-make] Error 2

I had already run sudo make mrproper. But it doesn't work. Kernel version is 6.4.0-rc3+

But when I don't use O= it works perfectly. How can I get the report without
specifying the location with O= ?