Without a screenshot, it’s challenging to visualize your issue, leading us to speculate. If I were to guess, you imported a hollow body object into the slicer.
Since you didn’t specify the model source or file format, we must continue guessing. Judging by your last statement, you have access to CAD software. Depending on how you designed and the file format you chose when you exported your part, it could be either solid or hollow.
Regardless, the slicer will follow your instructions. If you have a solid body and cut it, it will have solid ends. Alternatively, if you created a cut in the slicer software on a hollow body, you would have likely gotten a non-manifold error message, it would result in a model with incomplete edges, leading to unpredictable outcomes. If you did not get the error message then that indicates you cut a hollow object and the slicer simply obeyed the object geometry.
What I might suggest is to practice using the cut and connector functions on a primitive object that is generated by the slicer. A cube, cylinder or cone can serve this purpose.
There is a solution for that. It’s called “Computer Aided Design” or commonly known as CAD. Slicers are not CAD.
There is a way to cap off the end of a part using the slicer but such a tutorial would span many screens and I sense by your tone in your post, you wouldn’t be interested in such a solution anyway, you simply want a button.
One thing you may not have picked up on Bambu Studio, if the feature request does not sell more printers or bolsters there Bambu World site or sells more filament, Bambu will simply ignore it. You’d be much better off suggesting it to the Orca team but given the recent Bambu Shenanigans with Bambu Connect, the Orca team has sadly decided not to follow Bambu going forward.