Cutting image borders

[rich2005]

As you guessed there are several ways, especially for a png with transparency.

For that type of image:
Image -> Crop to Content
or
Image -> Zealous Crop

An alternative where there is a distinct transparent border.
Layer -> Transparency -> Alpha to Selection
Edit -> Copy
Edit -> Paste as -> New Image

All of those in 30 seconds https://i.imgur.com/E5CrYFe.mp4