This is pretty squarely marketed towards current users of 27" iMacs and iMac Pro's, so from that perspective the "modularity" being spoken of is the ability to

This is pretty squarely marketed towards current users of 27" iMacs and iMac Pro's, so from that perspective the "modularity" being spoken of is the ability to use the display with things that aren't the Mac as well as the ability to upgrade the display. Thunderbolt 4 also makes it better than the previous TB3 iMacs in terms of external expansion.