Optical images of the SMBHB candidates. The cutout images were retrieved from the Legacy Survey Viewer with a pixel scale of 0.15 arcseconds per pixel and are centered at the SRG/eROSITA X-ray position of the candidates. We highlight the X-ray position with a green circle with a radius of 3″ that corresponds to a typical 3σ positional uncertainty and the optical Gaia DR3 positions with a red diamond when available. Two sources (eRASSt J1522-3722 and eRASSt J0818-2252) are outside the LS footprint, therefore, we show the DSS images. eRASSt J1003-2607 was not detected by Gaia DR3 since the tentative source position highlighted inside the green circle is a faint source with a LS DR10 magnitude of m_r∼22. A 10″ scale bar is also shown at the bottom of the images for reference. All images are oriented with north at the top and east to the left.