I use CD keys fine. Another option, slightly involved, but may work out a win overall, could be worth buying it via MS Game pass rather then through CD keys. Will work out cheaper then 60 Euros I expect and you get the MS game pass for 3 months.
You can get MS game pass ultimate for 3 months for £1. As part of the MS game pass you will get access anyways to normal version of Forza free and the entire gamepass catalogue for 3 months.
However, you can buy Forza ultimate and as you have the game pass it will apply a discount to the purchase so you can buy Forza ultimate to keep for £40.
Above is in £, but I imagine the Euro's will be similar or close too anyways. I cannot imagine forza ultimate being available for £40 (well £41 if you add in 3 months game pass) to being over 60 euros.