Welcome to the community. 
The creator of that trainer, @MrAntiFun, is certainly not retired.
However, the trainer itself has been retired and will no longer be updated. This is because Forza’s developers have added a new anti-cheat that causes issues when using the trainer. Attempting to use a trainer on Forza Horizon 5 will always cause the game to crash at start-up.
All trainer developers on the internet have retired their Forza Horizon 5 trainers and will no longer be updating them.
This is made clear in the official threads for the trainer, for example: Forza Horizon 5 Cheats and Trainer for Xbox - #386 by Chris.
And other related threads: Forza Horizon 5 crash on start up - #23 by AussiePixelBit