I kept digging and think I've found a solution.
Set recording for RAW + JPG
RAW to card 1 and JPG to card 2
After taking the shot, press the playback button. On the top right of the LCD, the image filename is shown along with which SD card is being displayed. Switch this to display card 2 (jpg) and bingo, the 100% magnification is now available. To switch to SD card #2, press and hold the play button a second time (after the initial press to review the image).
WaltD got a reaction from George_P in How to review X-T2 images on LCD at 100%