You should be able to attain target watts at 100% intensity when your fitness signature is dialed in. Where SMART comes into play is many workouts in Xert’s library don’t use traditional %FTP for the target interval. Instead, they use a combination of target values scaled to your individual fitness signature. See if this thread helps answer your question –
Confused about SMART workouts? - General - Xert Community Forum (xertonline.com)
Best advice I have is to spend some time with the Academy series videos to quickly learn what is different about Xert and why. They are meant to be watched in order (building blocks) but you can skip around if you need to.
Also, this thread has lots of general tips regarding the Xert platform –
Beginner questions - Support - Xert Community Forum (xertonline.com)
Welcome aboard. 