Sourdough too wet to shape

I would really appreciate some help with my sourdough! The main issue is that, as I knead it, it becomes wetter, and eventually impossible to shape. Im not a beginner baker but a beginner with sourdough. I have a 100% hydration starter. Recipes is as follows: -75g starter (float tested and doubled in size - fed the night before 25g starter, 100g bread flour, 100g water from the kettle- cooled down) -400g white bread flour, 100g wholemeal -400g luke warm water - 10g salt Process: Mixing the dissolving the starter in the water, adding the flour and then mixing to a rough dough. Leaving for 20 mins, then adding the salt and throughly mixing. Slap and fold for 5 mins, leaving for 30 mins. Repeating slap and fold 5 times. Then stretch and fold until the dough becomes tight. Leaving for 30 mins between each, and repeat fives times again. At the end, I'm leaving it for 45 mins, then doing a pre shape and leaving for 20 mins before trying to shape for the banneton. I start to have about 2/3 through the knead. Dough seems perfect, but as I knead it becomes harder to handle, and impossible to shape. As I do it just spreads out and it's impossible to build up any tension in the dough. Prooving seems fine, I see lots of bubbles and activity. And I know the dough is expected to be wet, but it's impossible to shape! As soon as I turn it out it just spreads. It's impossible to slash as well, the slash just sinks away. Pics show the dough after a slap and fold, and you can see it holds some shape but spreads out again, and hold less as I go. If anyone is able to help I would really, really appreciate it! All happening at room temperature, about 21/22 degrees C. Thank you!