I had the same problem and It was so challenging. It always looked unfinished and I felt like people would fall off of the edge of the deck. Plus our dog insisted it was a dog run which was kind of gross. We found a work around. We bought a fence screen from an online store that offers next day delivery (website to remain unnamed. :-) They come in different lengths, height and colours. (Forgive the mess. We were prepping the spot in front of the equipment to extend the concrete pad and address the gap) The fence screen we are fast an easy install and this fabric doesn't fade or rip. It allows air to flow through but keeps dirt from going through the fence. After I dug a trent for the trees, I ran the landscape fabric over stones that we placed along the bottom of the fenceto create a basin. then back filled with soil. Fence fabric https://www.amazon.ca/Windscreen4less-Privacy-Grommets-Warranty-Customized/dp/B001OJXVKW/ref=sr_1_7?crid=LGXTY2DJMA7U&keywords=fence%2Bscreen&qid=1652055342&sprefix=fence%2Bscreen%2Caps%2C121&sr=8-7&th=1 The chainlink acts like the retaining structure, the fence screen helped to keep everything on myside and the landscape fabric, wood and stone helped with drainage. We have a 20" drop from deck height so we didnt' have to dig down too far to plant cedars and we could fill up the gap with soil. To break up the green we had cedar privacy screens, strategically placed to be over drainage, and grounding wires for the pool. I plan to plant hydrangea bushes at the base of the cedar screens but my husband wants hicks yews (no maintenance required and all around greenery for those of use who have cold weather 8 months our of the year).

What was the outcome. We are currently having a pool repair and have the same problem. I feel they are using the wrong coping size. The men doing the tile work said it was the wrong size but the pool company told them to put it in anyway. They want to send someone tomorrow to caulk.

Are the cabinets level in each direction? Meaning -- is this the wall out of plumb, or the cabinets? If it's the wall, I think your best bet with a gap that size would be to replace the countertop with one that can be custom fit to the wall along the back side. Butcherblock would be one inexpensive option, assuming you have woodworking tools (Ikea carries butcherblock for a very reasonable price). If you can't cut the top or have someone else do it, then you could use a separate backsplash -- not one that is part of the countertop -- and depending on its thickness it might cover a lot of that gap. Tile wouldn't cover much, but a butcherblock or laminate one would be about 3/4" thick if memory serves.

The gaps are there for a reason. They help prevent water from pooling on the surface and allow air flow to dry out the boards evenly on all sides. They also give the boards room to swell and shrink in response to changing humidity. While 1/2" gaps do seem excessive to me, boards without enough gap spacing are far more likely to cup and buckle as a result of changing moisture levels.