A new leak indicates that the X100VI set to launch on February 20 will be bigger than the X100V, although it may barely be noticeable. However, looking at previous Fujifilm trends, weight may be a bigger concern from the new move. https://www.notebookcheck.net/Fujifilm-X100VI-IBIS-leak-dispels-size-concerns-confirms-negligible-footprint-increase-for-compact-APS-C-powerhouse.797270.0.html
The X-T5 has IBIS and is smaller than even the X-T3 in height and width. Depth is possibly the only meaningful factor.
Strictly speaking X-H1 was the first body in the lineup to have IBIS. Not X-T4.