Blossom End Rot
This is not blossom end rot. It is anthracnose, a type of fungal disease. The following page has information about anthracnose in tomatoes and what you can do to manage it. https://extension.umd.edu/growit/anthracnose-vegetables
We recommend that you pick tomatoes before they become fully ripe. When they are allowed to fully ripen on the vine, they become more susceptible to problems when their skins are softening. Leave them to finish ripening inside.