Cubase will use all tracks that one can hear for regular playback.
Can you please state which version of Cubase you use (e.g. 12.0.70) and which edition (e.g. Cubase Artist)? Maybe also OS and which audio interface is being used.
A screenshot of the mixdown dialog would be helpful as well. Unfortunately as a newcomer to this forum you don’t have the access right to upload any graphics.