The originally submitted URL (https://www.catalyzex.com/paper/arxiv:2004.00626) points to

https://github.com/senguptaumd/Background-Matting, which points to

https://grail.cs.washington.edu/projects/background-matting, which points to

https://arxiv.org/abs/2004.00626, which points to

https://arxiv.org/pdf/2004.00626.pdf, which is inlined at the originally submitted URL. I'm not sure what's going on here, but on HN the convention is probably to link to the project home page first, and after that maybe the Github page and if neither of those exist, to the arxiv.org homepage (but not the pdf since those change with each revision). So I've changed to the project home page for now.