Your solution is very interesting but I think that it causes some flickering when the form is being resized by dragging one of its edges or corners. Looking at your code I guess that this happens because the resize event occurs constantly during this operation and the form is being maximized and restored alternately .went back and review the sequence of events of the form.
when you double-click the title bar of the form, the Resize event fires.
so I capture it and direct it to my user defined sub.
there is no timer, no class, no subclassing here.
uses api to get the mdiClient of MSAccess.
32bit and 64bit mso compatible.
also tested on MSA 2019 x64. .