Besides resetting the counter, what other actions might be needed to fully resolve the 5B00 error?

While resetting the waste ink counter software-wise is a common step, the underlying issue is a full ink absorption pad. In many cases, the pad will eventually need to be physically replaced. Some users attempt to clean the existing pad, but this is a messy process and may not fully resolve the issue if the pad is beyond cleaning. Replacing the pad is the most definitive solution.