At 3.22.3 I have a slope raster (32-bit floating point, single-band tif) derived from a DTM. I display this using a discrete interpolation, with three value ranges: 0-20, 20-40, and 40-90 degrees. These three ranges are symbolized with blue, green, and red, respectively. However, I require that the blue color be displayed with 25% opacity, as shown in the screenshot below. Green and red have opacity = 100%.
When displayed in a Print Layout, the blue color with the 25% opacity displays correctly in both the map and in the Legend Properties, screenshot below.
But note that the map legend patch does not honor the 25% opacity. Instead, a solid color is displayed.
There is a Github bug report with a similar problem, but it was closed without resolution two years ago.
There is also a SE GIS post from 4 years ago, again without resolution.
How to force legend patches to honor opacity settings?