Transparent Background "Bleed Through"

Hello! I have no experience with PSE 2021, or anything like it, and yet here I am trying to make a gift for someone by using it! I am working on pics of a white dog sitting in a sunbeam on an off-white sofa, and the same dog sitting on a box with magic marker writing and labels on it. I've tried numerous tutorial techniques to create a transparent background, and they all work to varying degrees, but in every image there always remains parts around the finished product which are dark smudges. Adjusting contrast using curves doesn't work at all due to lack of contrast on the original. I can't seem to get those cleaned up. The most recent technique I'm trying to use is: Select Subject, Select Lasso Tool to Add & Subtract from Selection, Refine Edges - "Paint" around image to mask background, adjust feather, contrast... Parts of every pic where there is heavy shadow, bright sun, subject & background close in color, reflective tape, dark writing, tile grout lines remain as lines and/or smudges. I've selected outputs as Selection and New Mask on New Layer, then tried to go back over the areas, but I can not find anything that works. Any and all suggestions would be appreciated. Thank You!