Is that 300-1000 unjustified deaths, or does it also include situations where the use of deadly force may have been reasonable?
Filtering for "2019, black, unarmed" you get:
15 people shot and killed by police match your filters (less than 1%)
Change that to "2015" and you get:
38 people shot and killed by police match your filters (1%)
People are also marching for deaths caused by other citizens that were first swept under the rug, like Ahmaud Arbery.