How can I restore outdoor walk as workout option on my Apple Watch Ultra?

Outdoor Walk was a workout I invoked frequently on my Apple Watch. I hadn’t used it for a couple of months, and now when I need it, it has disappeared. How can I get it back. It does not exist in the list displayed under the Add Workout option.

[Re-Titled by Moderator]

Original Title: Outdoor walk has vanished from my workout options - How can I restore?