The ‘or don’t’ is the important part. Writing a sequel is something most writers wonder about, plan for, or find sneaking up on them, but one can actually start a brand-new story as if it were the sequel (see George Lucas’s A NEW HOPE . . .).
By treating your new story as the sequel to another story, you are catching up a reader on the world you have created, as well as creating mysteries and allusions to events and actions that should spark your reader’s interest.
Alternatively, if the story you have planned but are struggling to write, perhaps you avoid its obstacles by making it the past and forging ahead with the aftermath of that adventure.
Another great example of a sequel-type story that isn’t a sequel is FRIEREN BEYOND JOURNEY’S END, which sees an elf joining a new party of adventures while reconciling and recollecting her previous party, which defeated the Demon King.
By embracing the idea that your characters and world have already experienced some great adventure, you create a shorthand of world-building and depth to call upon, just like much of current history is informed by the past.