Does anyone know how to open a .rar file?
If 7-zip couldn't open the .rar it's probably because it's corrupted or because it has a key, in which case winrar will also fail.
In these cases, it is better to directly contact the person who uploaded the game and tell him about the error when decompressing.
PS: I have been using 7-zip for many years and it has never given me any problems.
It is the first time in my life that I hear that. I know that sometimes winrar can open corrupt files (it seems winrar can fix errors or at least ignore and unzip) while 7zip needs the file to be uncorrupted. but the problem is a corrupt file and if that happens to you in itch, it is better to discuss it with the developer.
EDIT
PS: I don't doubt what you're saying, what I'm saying is that if 7-zip can't open a .rar, it's probably a problem with the file and instead of looking for ways to bypass the problem (there are programs that can fix errors like a bad CRC) it's better to inform the developer.
Perhaps .rar files have more than one setup or configuration and 7-zip does not recognize all of them? I dunno. Grasping at straws here, but I stand by what I said; it only happened a couple times for me.
I would rather post a .zip file or maybe a .7z file on here anyway, for the sake of better compatibility. On my site where I have a hundreds of bundles, they are all .zip files, since it's something (pretty much) anyone can open.