This is a small 50x50x50 mm box I designed that prints completely flat and is then folded and glued together (this can be optional with version 2).

I used B7000 glue (https://s.click.aliexpress.com/e/_c3Mn9v7l or on amazon https://amzn.to/4uEWwF4), and it glued very well and quickly, other glues might work just as well. You can use four rubber bands to hold the box together while the glue sets.

There is one single body that is white. Select it (click on a tab, for example, to find which one it is in your slicer) and change the color, then select all the others and change them to the second color of your choosing. Print at 0.2mm layer height.

When folding, make sure you go slightly beyond 90 degrees so the resting position ends up being 90 degrees.

I only tested this with PLA. Make sure the infill lines are not parallel to the folding areas, or it will break when bending.

Edit: I added an additional file with two extra tabs for the side walls so there is no gap when the box is closed.

Edit 2:

I added V2, which changes the tabs and adds an additional one-layer tab that folds over the top of the side tabs so glue is optional (especially if you tie a ribbon around it).
I also added a plain version without the mosaic design so you can quickly print it to test.