config.txt
...
hdmi_drive=2
hdmi_ignore_edid=0xa5000080
hdmi_group=2
hdmi_mode=87
hdmi_aspect_21_9=7
hdmi_pixel_freq_limit=400000000
hdmi_cvt=2560 1080 50 7 0 0 1
max_framebuffer_width=2560
max_framebuffer_height=1080
framebuffer_width=2560
framebuffer_height=1080