Hopefully in a future update HDMI support for this monitor(resolution?aspect ratio?) for the Rpi4 will be added.
Unless someone reports it upstream, I don't think it will be magincally solved.
Someone reported something similar this last year and for them it has been solved with a firmware update, see https://www.raspberrypi.org/forums/viewtopic.php?f=28&t=248037&start=25.
If the recommendations in that topic won't solve your issue, then I suggest replying to that topic and adding your own monitor EDID for the RPT engineers to check it.