I didn't change anything purposely. Might have accidentally hit a hotkey??
You have some abnormal and unwanted behavior!
First thing to do, is to check your Normals!
If you go to your Viewport Overlays dropdown menu (those two 'yin yang-like' circles, top right of the 3D Viewport), under Geometry, check Face Orientation. Everything should be blue. If you see red , select those (red) faces (of course in Edit Mode) and press ALT+N to bring up the Normals menu and choose Flip (or press F). Alternatively, go to Mesh > Normals > Flip.