To unlock the Infinite Number Of Realities trophy in Trials Rising, you will need to progress through the main game's career so that the
Ghost Town track is available in the Sixty Six DLC.
On the track, progress to checkpoint two. Shortly after passing checkpoint two, you will be able to see a moose head on the wall in front of a large drop. Bailout and touch the moose head, which will make it turn purple.
Respawn at checkpoint two and progress to checkpoint three. After the large loop section, slow down and instead of making the jump across the gap, drop down and ride into the hole with the purple smoke coming from it.
Complete the track and the trophy will unlock.
You can see a video of how to unlock the trophy below (credit to Hairy Cabbage on YouTube):