I was installing a Sanicompact Pro toilet and "oopsied" by cutting open the wrong pipe. Solution? A 3D printed TPU plugg that gets screwed into place with a hose clamp of the appropriate size.

See picture of the instructions about what pipe that I accidentally cut. Marked in red. It's been a solid solution for over 2 years now.

I pretty much printed it with: TPU 4-6 walls 4-6 top/bottom layers 45% infill 0.2mm layerheight