In this image, I have selected the "spam" option. As you can see, the radio buttons are totally invisible.
Forum bug report -Radio button on forum report screen not visible
Been like this as far as I remember honestly—not really a big deal.
Just click on the option and then on submit, it'll work.
No, it's not a big deal. But it is clearly unintentional, and bugs that don't get reported don't get fixed. I don't see anywhere else to report issues with the forum, so here we are.
Most probably was fixed in a newer version of NodeBB. Unfortunately all migration attempts on test system failed so far due to some very specific quirks in NodeBB and our setup. And currently other things have higher priority 
So thanks for the report, all we can do is wait until I find time to finally update the software.
"Nerds have a really complicated relationship with change: Change is awesome when WE'RE the ones doing it. As soon as change is coming from outside of us it becomes untrustworthy and it threatens what we think of is the familiar."
– Benno Rice