Choosing “Wait and see” during the Saiyan Rampage episode will place Jiren on a new path. A majority of the fights will be different and he’ll have an important encounter with Master Roshi. All of this comes to a head at the same final battle, however, which still functions identically. Even the alternate objective is completed the same way.
To unlock the True Strength ending, you need to beat everyone quickly and the alternate objective needs to say “With Master Roshi defeated, defeat Frieza, Android 17, and Goku.” If it just says to beat the three enemies, you’ll need to reaffirm your choice back at the first episode. Defeating them fast enough with the right objective will treat you to a fully animated cutscene involving Jiren making a wish with Super Shenron.
It’s unfortunate that unlocking these Dragon Ball: Sparking Zero endings can be so perplexing. They’re not the craziest that the story mode has to offer, but they’re still enjoyable. Seeing them all provides two achievements, as well as a full set of Dragon Balls for Super Shenron, which is great if you’re trying to unlock additional characters or some unique ability items.