For first you should try the usual things every support telling you out:

1. Are you meet minimum settings? check here
2. I you don´t use Admin Windows Account start Game as Admin:
open filebrowser, go to your steamaccount folder, exactly to here: \SteamLibrary\steamapps\common\ForzaHorizon5. Now right click the "ForzaHorizon5.exe" and choose: run as administrator.
3. Update your Graphics driver.
4. Disable NVIDIA in Game Overlay (May cause problem but usually not)
open GeForce Experience, click the gear button in the top of window and disable "InGame Overlay" in the left hand of window.
5. Validate your gamefiles
in Steam Libary rightclick on Forza Game and select propertys. In the propertys menu, select "Local Files" from the left hand panel and at this page select "Verify integrity of game files". Steam will do the rest.

especially when problems appeared after update this works, the thing is it´s not a problem of game itself it seems.
I suggest the issues for forza come alive cause the game update may broken some windows files when installing.

So to get lost of most crashes try this out:

In Windows Task Bar click in the search field and type: The command prompt app will appear on the left, RIGHT CLICK it and choose "run as administrator" and choose "yes" if it ask for admin rights.

Now the App starts Up, what you see is this path:
C:\Windows\System32> followed by a blinking cursor.

Just type or copy paste the following text: and press the return button.
Windows starts a system scan, wait for it to finish...

If it found some damaged files and repairs it, it´s a good sign.

After it´s done restart you pc for first.

Now test your Forza Game and be Happy ;-)

Problems came back later, not everytime but sometimes.
So again i searched what may cause this and my aim goes to controller.

Disabling it made things fine again so here it is if ya wanna try it:

In Steam Libary right click Forza, then choose "propertys"
Now open the register for controller in the left and disable steam controller configuration for this game.

And that´s already all, it´s done in no time.

That´s all, I hope this helped you out of that frustrating crash situation.
I´m glad if I was able to give you a hand and will be very proud and So, let´s meet back in Forza´s Mexican streets, have a nice day.

Greetings by FH5´s Darktr3p!