Forza Horizon 5

Most of the challenges are straightforward, win races, do drift PR stunts.
Pinning the challenge tells you where to go, and what to do exactly.

The only challenge you may have trouble with is the SPEEDEASY challenge where u have to get 10 speed skills in Grit Reapers Events.
(I completed the whole DLC but only managed to get 2/10.)

SPEEDEASY challenge made easy:
If you Pin the challenge you can see the counter realtime.
1, Start the rally version of: RESERVA DEL CARRIZO
2, Use any fast car, like the Koenigsegg Jesko
(I used the 2019 Brabham BT62 car with an S2 tune)
3, Struggle your way through the first part of the track then you reach a long and "straight" road section.
4, Here you can get enough speed to get 2 Speed skills until you reach the left turning end of the road.
5, Then you just rewind time until you are at the beginning of this whole road section.
6, Repeat steps 4-5.

The basic complete/win each race challenges can be done with auto-drive on tourist difficulty if you are feeling lazy (as I was). So I won’t address those specifically. I used the Subra WRX STI 2015 [Auto Upgrade B] for the majority of them. I usually did the race first, then the rally second (and did any race specific challenges then with no other cars to annoy me).

For Drift Zones, I used the 1932 Ford De Luxe Five-Window Coupe, with anti-lock brakes, traction and stability control off. Tune 489-519-306

For the list below I’m going to assume that you’ve already won all the races, and 3 starred all the PR stunts. I also won’t cover any that are just “win race X in a certain car or car type”.

Grit Reapers
2-Lights Out: See “Absolutely Smashing” in level 8
2-Rally Photography [#2 Audi Sport Quattro S1]: Just take a photo Anywhere.
2-Bye Bye Cacti: you probably have this already from just driving off road, if not, go to the desert.
3-Driving With Style: You most likely already have 10 drifts without even trying
3-Don’t Stop!: Again, already had this just from racing normally. Reserva Del Carrizo is an easy race to do it on because of the long straightaway.
3-I Said Night: See “Absolutely Smashing” in level 8
4-South East Recce: I used my B class Impreza again. I only had 20 seconds to spare, but you could use a S1 upgraded car in the Modern Rally class to make this even easier.
4-Recce Complete: Same as the base game, just clean up any dark spots on the roads you haven’t found yet.
5-Did Somebody Order A Warthog?: This should be easy as long as you pick a Warthog.
5-Crateres Secos Challenge: (2003 Nissan Fairlady Z Forza Edition [761-570-369]): This one you will actually have to drive, but it should be too hard. Go as fast as you can, on the areas with no solid barriers, go as far off the track as you need to in order to turn at high speed. Use rewind if needed. I finished with about 10 seconds to spare on my 1st attempt, with some minor rewinding. A friend used the McLaren Extreme E which may be easier.
5-Retro, Meet Retro: Travel to the hairpin by the V in “Cave Paintings”. Your car needs to be right under the snake painting (like up on the dirt hillside) and the shot needs to include the whole painting.
5-Car Wash: Start at the bike track and just drive cross country to the Cascada Fuerte Waterfall. I had 1:25 left so there is plenty of wiggle room.
6-Night Watch: See “Absolutely Smashing” in level 8
6-Drift Dual: I would pick a fast car rather than a drifting car for this. Just one star at Tierras Verdes (45k) then get to Canyon Sweep (35k) for another.
7-Speedy: I got this without even trying or noticing. Reserva Del Carrizo is an easy route to pick up a couple on due to the straightaway.
7-Drift Champ: You should easily get this while 3 starring the drift zones, if not you can repeat one.
8-A Highly Skilled Grit Reaper: Win 3 Events against Highly Skilled Drivatars. I preferred race for this as it was clearer where everyone stood.
8-Speedeasy: You should be able to pick up one or two on Reserva Del Carrizo on the straight section. You can rewind and repeat the section to get all ten.
8-Absolutely Smashing: The solar farm in the NE is a great place to grab these but they only show up at night. You can change it to night by starting any grit reaper race and then quitting it.
8-Hold On!: Crateres Secos will get you plenty of air if you run it in a fast car.

Forza Horizon 5 Snake Cave Paintings Location - Take a Photo of any Retro rally car with the Cave Paintings