DIY Logistics Box Cat Litter Box Anti-Litter Leakage Snap Strip Cat Door Cat Hole (Semi-Open Cat Door)

No commercial use. I don't think many people will need this, but if there's enough demand, I can make a video tutorial.
The dimensions may look complicated, but if you buy the same logistics box and cut along the edges shown in the diagram (cutting along the edges, it can be slightly larger than the red frame but not smaller), it will generally be about the same size. Minor size differences can be adjusted with a utility knife or a soldering iron.

This was made based on my own logistics box cat litter box, suitable for a cat opening with a length of approximately 217mm (minimum), height of approximately 200mm (you can cut it in slicing software or print it out and cut it directly with scissors), and a width of approximately 17mm (maximum). The supports are a bit difficult to remove, but since they are on the inside, it's okay if they aren't perfectly clean.
The dimensions are quite precise. To minimize future displacement, the top outer edge is 20mm wider than the inner 17mm thickness, and the model has an internal buckle. Therefore, to insert it, you need to forcefully spread the edges apart and snap it in. Mine was pushed in with force and didn't break. It's best to print and insert it while fresh for optimal model elasticity. After a few months, the model becomes brittle and can easily break if forced in this way.