Their arms are small, but beyond that there’s basically nothing similar between them and an ostrich’s wing. The muscular anchor points are not similar at all to winged creatures, who require significant musculo-skeletal connection to the breastbone even in mostly vestigial wings. You can see this in the ostrich skeleton as the large “blob” of bone in the middle of the rib cage. There is nothing similar in the T-Rex. Even more of a problem with this theory is that the T-Rex’s popularity is in large part due to the fact that we’ve discovered a fairly large number of T-Rex fossils in good condition and not substantially disturbed… It’s why we have famous models like “Sue” and “Black Beauty” that make such good displays in natural history museums. Unless you’re proposing that a dozen different skeletons from several different regions with different ages all had bones shift after death to end up in the same position…

Our knowledge of what dinosaurs looked like is not perfect, but we’ve also come a very long way from the Magdeburg Unicorn or horned Iguanodons of the 1800s. Paleontology has largely moved past “puzzle piece” biology, where things are just haphazardly thrown together because they kinda look like they fit. There’s comparison to other species - not just reptiles- to see what are comparable modern equivalents or to other contemporary animals. There’s kinematics and musculature considered. Unless some fossil discovery is made that completely upends the evidence we have now, at least in the case of skeletal articulation of well-known and well-studied species like T-Rex, we can be reasonably confident that we’ve got it pretty close when it comes to what their skeletons looked like.