Solar Orbiter’s STIX has observed over 1000 flare candidates as of September 2021. Of those, 358 are given locations by the Coarse Flare Locator. Joint visibility with Earth-orbiting SDO can be determined using ephemeris information from Solar Orbiter, contained in the Spice kernels, and the Earth. Code is here.
The 24 jointly visible flares are plotted below, with additional information available through the hovertext.