EDIT: I found the solution, “Added basic alpha compositing support - Alpha is available afterpostprocess when using FP16 buffer format.”, stated here Changelog | High Definition RP | 9.0.0-preview.71
I retract some of my frustration with Unity 
I’m just upgrading to HDRP, coming from the Standard/builtin pipeline. Most things seems to work alright, but there is one feature which I don’t know if its even possible in HDRP.
On screen debug graphs. I made something similar to this: [Graphy] - Ultimate FPS Counter - Stats Monitor & Debugger | GUI Tools | Unity Asset Store, but using a lone camera drawing to a render texture, then scrolling that texture in the UI. It lets me dra multiple one pixel wide graphs on top of everything with minimal performance hit, here is an example with a red and a green graph:
In HRDP this seems impossible since there the alpha channel is discarded in render textures: Unity Issue Tracker - [HDRP] Camera Color Alpha variable is ignored when using HDRP 5.10.0
This in it self is to me pretty unacceptable and ignorant of Unity to disable a core feature like and not give a good reason why. Like rendering a character preview in a UI with transparent background is seemingly impossible now. Unless you write a custom shader with a sort of chroma key functionality, but that is bad and ugly workaround in my option.
I don’t want to be whiny or sound too dramatic, but how is this a thing? What? Why? At least giva a reason!
Anyway, I’m getting of track. The LineRenderer does not work either since you need to use “Screen Space - Camera” mode in the canvas to make the LineRenderer appear in the UI. And when you use “Screen Space - Camera”, the alpha ignoring issue breaks everything again. A camera rendering a canvas in “Screen Space - Camera” mode overwrites the whole framebuffer since the alpha is ignored.
So, my graphs, does anyone have any idea on how to do this now? Drawing lines in the UI?