So, the guide Destrier works great if there is a community event avaliable, however half the time, there doesn't seem to be. Upon further inspection, and I'm not sure if this has always been the case or not but as of today (2nd March 2021) the achievement description on the Xbox App for Windows 10, on Xbox consoles themselves seems to be slightly different that what TA mentions. On Xbox it states the following:
"Finished a Stage in sunny conditions in Community Events or Clubs
So to make this super easy for those who decided to sign up for a Racenet account when they first opened the game:
Go to https://www.dirt4game.com/
Click the top right where it says "PROFILE", and then login, choose your Microsoft account as the login option and follow the instructions/accept the EULA/T&Cs. Once done, you should end up on the homepage again.
Click top left under "Online", followed by "Clubs", then on the next page you should be able to hit "Create a Club". Choose whatever name (this has to be unique) and handling style you like, the rest can be left default. Scroll down and click "Next".
You'll be thrown into creating your first championship, so click the massive "ADD EVENT" button.
Now choose whichever gamemode, country & vehicle restriction you would like on the left side, then move over to the right side, make the length as short as possible, and the complexity and low as possible.
Next comes the part you should pay attention to. Select Midday
in the "Time of Day" section, and Dry
in the Weather Section.
Scroll down, past the stage preview and just click "Save Event".
On this next screen, just press "Continue to Step 3", followed by "Done" on the next page.
Now, open up DiRT 4 on your console, navigate to "Events", "Multiplayer", "Clubs", and wait for it to download the data. You should see your club that you just created show up. Now just load into that stage, drive through it as fast or slow as you'd like and once you get awarded the XP from completing it, you should have the achievement pop.
Although this looks like a lot, its about a 3 minutes process on the website and another 5 minutes in game with loading screens etc.
This is one of my first guides so please let me know how I did and comment on why, if you did downvote it.