1. Your screenshot shows the screen blending mode is applied to the bottom layer in the layer stack. The blending mode sets how the layer blends with the layer(s) beneath it. Since there are no layers below the bottom layer then it will have no effect.
2. @CShubert I can replicate that issue in the current version (24.7) when using the slider for stroke width in the properties panel. If I use the equivalent slider in the options bar at the top of the screen it works as expected with a live pre
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