I think that the Ikea Lego BYGGLEKs should be parts in MECABRICKS even though they do not have official part #s. They are an official lego product and have lego studs and have a size that makes it so you can use bricks inside and around it.

Official website Ikea Lego BYGGLEK website:
https://www.ikea.com/us/en/new/play-never-stops-with-the-bygglek-collection-pub1955e4c0

Article with dimensions measured in bricks:
https://brickarchitect.com/2020/review-ikea-bygglek-lego-storage-box/#:~:text=The%20Large%20Box%20costs%20%2414.99,the%20ridges%20on%20the%20underside).