It is not neutral, it takes tens of years for standard sources of biomass to accumulate to useful amounts. Fast biomass would use something like hemp or other grass but it's still problematic.
And it does increase CO2 and NOx levels when burned, not to mention soot - it's dirtier than quality coal. The growth itself does not capture nearly enough to cover for it.
Biomass is mostly wood. If the forest is in steady-state (as is the case in Germany), this is carbon neutral. The main issue is that plants are much less efficient at light harvesting than solar cells. This means that there is probably not much scaling potential left.
And it does increase CO2 and NOx levels when burned, not to mention soot - it's dirtier than quality coal. The growth itself does not capture nearly enough to cover for it.