I tried several times to pick a picture from my phone gallery and set it as my WhatsApp status. But, whenever I try to do that I could only see a black screen with no photo gallery visible at all.
That seems like a glitch either your phone may have or a bug in the app itself. If it is your phone that is the culprit, then it can be easily fixed by either restarting or soft resetting your phone. A soft reset can be done by holding Volume Up button + Power button at the same time for about 10-15 seconds.
If, however, that didn't fixed your problem, then it should be a WhatsApp bug that you may report it to them.