Forza Horizon 5

Find the "Donut Low" story missions, which are located just left of Playa Azul (on the right of the main Mexico map).
There are 7 chapters, each of which you'll need to complete for this achievement. For another achievement (Give It the Beans), you'll need to 3-star each chapter, so you may as well do it all in one go.

1 - Welcome to HiLow

3 Stars - 1:52
This is shared between the Hi and Low stories, so you only need to do it once.
For the most part, you'll want to just follow the highlighted track on this first mission. You can try shortcuts but the first two-thirds of the race are through heavily wooded terrain, making shortcuts high risk.
That said, when you're a little over a mile (~1.6km) away from the target, there will be a sharp right turn. You can cut the corner here, then you'll be able to ignore the highlighted path and shoot directly across open fields of agave and cempasúchil (the orange flowers) in order to hit the finish line.

I finished in roughly 1:41

2 - Welcome to Low Team

3 Stars - 2:15
Super easy, there are no checkpoints here, so as soon as the race starts, follow the road into the first turn then veer off the road and aim straight towards the end goal. Find your destination marker and beeline straight towards it over fields and rivers. This is slightly harder than the "High Team" challenge, as there are more forests to navigate through, but they aren't too dense to deal with and you can always rewind if you do miscalculate.

I arrived in 1:21 ish.

3 - Every Car At Horizon Ranked

3 Stars - 1:40
A regular 3-way race. you have to follow the highlighted path a quickly as possible. There aren't any major shortcuts you can take other than clipping small corners wherever you see them, as the majority of the race has checkpoints that you must hit.
0:50 - 1:00 into the race, you should be hitting a large motorway/freeway that goes through a mountain and over a bridge. Once you hit this, keep your finger on to go as fast as possible as it's then essentially a straight road from there until the end minus a quick turn at the end. Do watch out though as there is traffic on that road.

I sped through a screwed up the last corners but made it in 1:38.

4 - Déjà Vu

3 Stars - 2:10
Another straightforward one.
There are no checkpoints here and you can go completely off-piste. Start the race and follow the highlighted path until you see Nolan join you from a road on the left. Instead of going forwards, take the path to the right (opposite from where Nolan joined) and follow that road around the corner. Keep following it until the trees disappear and the environment becomes more open, where you should see the destination marker in the distance directly in front of you.
Head directly to the marker, but as you approach the city of Mulegé, the car will start to smoke and slow down. Make sure you dodge the houses and structures around here to avoid being slowed, but you'll naturally get slower and slower as you approach the marker.

You'll likely find that Nolan will overtake you near the end too, as you're crawling to the finish line.

I finished in 1:54.

5 - Bumper 2 Bumper

3 Stars - 150,000 points - This is a drifting challenge, change any settings you need (like stability and traction control) before starting.

You start this chapter with 5 minutes on the clock. You first need to drive 3 miles (~4.8km) to the highlighted drift zone. Follow the road, but if you want to save time, when you're about 1.7 miles (~2.7km) away, you can launch forwards off the road directly towards the drift zone, then turn around once you reach the destination marker.

This drift circuit seems easier than the others in-game as you don't have to stay on the road for the points to count, although you can't stray too far away. If you mess up a corner or section, you can use rewind as long as the score still shows at the bottom of the screen. If the score disappears, and you don't hit 150,000 then you'll have to restart the chapter.

I'm not amazing at drifting so this took me a couple of goes, but I eventually finished with a score of 151,608.

6 - To The Rescue

3 Stars - 2:10
You're driving a lorry with your damaged car on the back this time, rather than the car itself. The lorry is pretty fast though. This is another where you simply have to follow the highlighted path and there are checkpoints for you to hit.
There are a couple of tight corners at the start of the race, but it's smooth sailing once you're past them. There also aren't all that many shortcuts you can take other than trimming a little off some of the corners, but you shouldn't need to do this.

I kept my foot on the accelerator and followed the road almost exactly and arrived in 2:03.

7 - Does More Expensive Mean More Better?

3 Stars - 1:25
This is the exact same task as Donut Hi.
A two-parter. The first stage of this sees you apply upgrades to and tune your own car. This is annoying, as while you're given a budget of 60,000 CR and a target of "A - 800", you have to hit this in a specific way.

Taken from the other guide (thanks to FatBlubfish219) and very slightly tweaked, use the following upgrades and tuning;

Press to go to upgrade menu.

Once you have completed the Tuning, PRESS TO SAVE IT. If you use to get back to the car upgrade screen, the tuning won't save and you won't ever 3-star the upcoming race.

With that all saved, back out of the upgrade screen and you should be told that the upgrade meets the requirements and is complete. Then drive a little to the right and wait in the destination highlighted. After a few seconds, you'll start a race.
Nothing special for the race, simply follow the highlighted track, hit all the checkpoints and you'll finish in time.
If on the long straight, you don't break more than around 135mph (~217 kph) then you didn't save the tuning correctly (you have to quit out the event and restart, then reapply all the upgrades and tuning).

I finished in around 1:22.

With that done, go past the screen saying you got 3 stars and as you load back into the freeroam map, you'll pop this achievement.

As always, if you place a negative vote, please let me know why so I can improve the guide.