As i understand the current consensus on Spinosaurus:
• it walked on all fours, not on two legs.
• it was probably similar to a giant croc as is mouth is design for catching fish.
• the tail looks like it could be used for swimming, but didn’t have the muscle attachments for croc/gator tail swimming.
• which is weird because that should put it in an ideal situation to give fantastic skeletons(similar to the duck billed dinosaurs), but we barely have any. Worse is that the most complete skeleton was destroyed by allied bombing in WW2.
• and all of that raises the question of what the hell was the sail for. Since that doesn’t make sense on an aquatic ambush predator.
• moreover, the sail wasn’t a one-off, but a feature of half of the spinosaurids, so it was selected for. So it served some useful purpose.