So this 'guide' doesn't 100% the game, it'll just give you all of the achievements that need a lot of grinding. I'm convinced these are only added to games to boost played hours, so I want to give people the option to skip just that.

Your save files can be found here:
<drive Steam's installed on>\Program Files (x86)\Steam\userdata\<steam ID>\621830\remote

You just download the files from the link below and paste them into the folder above.

All you're interested in is the save.dat file. Before doing anything, I highly recommend making a copy of it, just in case - or just rename it to save2.dat. After doing that you need to rename one of the files you downloaded to save.dat. Start your game and do the corresponding action, which will unlock the achievement. Close the game, delete the now unneeded save.dat file, and repeat the process for the rest. Once you're done you can rename your original save to save.dat and carry on doing what you were doing before.

Just to repeat, none of the files will instantly 100% the game for you. They're just a shortcut to the most annoying achievements in the game.

I migrated the saves from Dropbox to Google Drive, now the link works by just clicking on it:
https://drive.google.com/drive/folders/1IvtSgEIuuLN2jLncC9Xnx1ye5E5bPThc?usp=drive_link

Here are explanations for each file, although the titles should be self-explanatory:

Save - 45 min repair
Go to the quick games and continue the custom tournament there. Go to repairs and the car should be damaged enough for you to get the Manager achievement. Iirc the combination is 3x engine, 1x Steering and Gearbox.

Save - 479.66 km tarmac
You need 20 km to get 500 km on tarmac. The counter is a bit off, it might not unlock on 500 exactly.

Save - 496.92 km snow
You need 3 km to get 500 km on snow. I used Sweden's SSS circuit to grind this, so it'll likely unlock after a single race on that.

Save - 990 km gravel
I originally unintentionally unlocked this achievement without saving first, but FilipCZ9 was kind enough to give me a save file that's missing about 10 km to get 1000 km on gravel.

Save - 4956.18 km
A race in Poland's Kruklanki stage will unlock both the Nomad and Legend achievements.

Save - Spy + MP (grind needed)
This is a sort of raw save, for those that want to do the grind but can't get the Spy accomplishment. All multiplayer and the Spy accomplishments are completed, along with a some others, but technically the entire game needs to be played and all the grind still needs to be done.