Call function with * bitmap parameter

If one was to look t the documentation for the u8g2 library one may find

void u8g2_DrawXBM(u8g2_t *u8g2, u8g2_uint_t x, u8g2_uint_t y, u8g2_uint_t w, u8g2_uint_t h, const uint8_t *bitmap

Which explains why String is not working.

u8g2reference · olikraus/u8g2 Wiki (github.com)