Unusual insomuch as it isn’t usually associated with close up shots but is used to give distant objects a toy-like appearance.
To put it in a nutshell this type of filter allows for an in-focus strip with either side blurred.
Many photo editors now have a tilt-shift filter but the level of sophistication varies dramatically. The simpler ones allow for the in-focus strip to be positioned anywhere along the horizontal but that is about it. More useful ones allow for the amount of blur, the transition area, the width of the in-focus strip and position of the strip (including diagonal and vertical) to be chosen. The very sophisticated ones allow for bokeh circles and even aperture types to be added.
I like the middle approach as that allows for enough flexibility without requiring a day and an online course to produce a finished photograph.