I brought in the i9-9900K.
Certainly a possibility exists. A practical approach would be to run the CPU on a different machine if feasible.
The only device I have is the one likely not compatible with it, as indicated by the title explaining my confusion about the B250.
The circumstances are quite bad. The most reasonable choice seems to be sending the CPU back to the seller. I wonder if that's an option.
It's really annoying when the system struggles with just 1 stick of RAM but has 8GB available.