Here's an oldie-but-goodie from Laurel's Kitchen...
Mix two parts vegetable oil with one part liquid lecithin, shake
well. Store in refrigerator. Brushed on to any pan, NOTHING will
stick to it, not even the loosest sourdough!
That said, if you have a spray product you like, spray it right onto
the loaf after you've shaped it. Hold the shaped loaf top-down in
your non-dominant hand, spray sides and bottom. Be sure to get the
ends. In this way the entire surface of the loaf that's going to
touch the pan is protected, and it takes a fraction of the time
compared to painting a pan carefully. (I rely on the "Everbake"
cooking spray, King Arthur carries it.