Having trouble with blurry or "smudged" pixels when I try to edit assets

[SapphireBandit]

Hi, I’ve been developing a short game since October of last year as a way for me to learn Unity, and to do this I used the free asset pack, “Pixel Adventure 1”. However, I wanted to create a makeshift line border during development, so I would have more options for sprites to use. Everything went fine when I plopped the sprite into an editor(originally Photopea), but after I save the file to windows the pixels turn from sharp and defined to blurry and smudged. It gave me a lot of grief many months ago, but I eventually just left them as blurry so I could actually develop, saving the problem for later. Well, later is now, and I’d love to know how to fix this. I tried using Piskel recently to see if it was just the editing software, but nothing seemed to change. It would always go blurry right when I save it as a file. Also, if it is relevant, I like to do my work on a school issued chrome book as it helps me focus(don’t worry, I have plenty of external backups and no performance problems), so maybe I’m running into a problem there? Below I have screenshots of how I edited the file in both softwares as well as the comparison between the refined and blurry edge, if anyone knows how to fix this please let me know.