Hi Luciano,

you can filter courses by Reactive development. All of them are useful.

Adding to it, you have a Tech Talk talking about Reactive:

https://www.outsystems.com/training/lesson/2104/tech-talks-2020-converting-existing-portfolio-to-reactive

In my opinion, besides the courses you should also read the documentation available and practice everything in Service Studio, testing scenarios, checking each property, etc.

https://success.outsystems.com/Documentation/

Regards 

I think you go this 

https://www.outsystems.com/training/paths/18/becoming-a-reactive-web-developer/

this is the best way to to learn most specific for test..

and for Test practice purpose go this link

 https://danilo-miquelino.outsystemscloud.com/QuizOutsystems/Reactive

for more practice go throw this link...

https://quizlet.com/570137215/outsystems-becoming-a-reactive-web-developer-flash-cards/

and also you practice all small small things in a practical way so you understand very deep in conept 

basically Entities and relation this is the most important according to Test..

keep studying ..Best of luck for your certification Test..