WASHINGTON — Vice President Kamala Harris is announcing a plan to give Black men more economic opportunities and other chances to thrive as she works to energize a key voting bloc that has Democrats concerned about a lack of enthusiasm. Harris’ plan includes providing forgivable business loans for Black entrepreneurs, creating more apprenticeships and studying sickle cell and other diseases that disproportionately affect African American men. Harris already has said she supports legalizing marijuana and her plan calls for working to ensure that Black men have opportunities to participate as a “national cannabis industry takes shape.” She also is calling for better regulating cryptocurrency to protect Black men and others who invest in digital assets. The vice president’s so-called “opportunity agenda for Black men” is meant to invigorate African American males at a moment when there are fears some may sit out the election rather than vote for Harris or her opponent, Republican former President Donald Trump. The vice president unveiled the plan ahead of a Monday visit to Erie, Pennsylvania, where she will visit a Black-owned small business and hold a campaign rally.