I'm not sure if it varies by trim levels, but in both my 2016 and my 2018, this shows up in one of the screens on the MFD (section 3-45 in the second link @HeyChris linked above, but it sounds like you looked at those) - the one up in the middle of the dash above the radio (not the one in the speedometer, if you have that). What trim level and year is your Forester? I seem to recall something about base-trim 2014s or similar didn't have the full MFD capability, but I'm not 100% sure there.
Something you may need to do is go into the menus and configure the displays -- as I recall, the "miles-to-empty" portion is something that is one of the many options on one of the screens (though I think it is default on several). It's possible it has just been turned off and you need to turn it back on (or reset the displays).