NX-Shell VS mtp-server-nx

You might be able to access the save files using a Switch file manager like NX-Shell.

I recommend using a file manager like NX-Shell though since you can do all this directly from your switch without using a PC or phone. You can download it from homebrew store or https://github.com/joel16/NX-Shell/releases.

In addition to what others have said, if you really have no other options: https://github.com/joel16/NX-Shell

So I'll repeat my suggestion. Clean up the files using NX-Shell. Presumably you don't have a Windows PC handy or else you would have already fixed it, so there's a solution you can do right on the Switch itself.

NX Shell says it supports extracting zip archives - https://github.com/joel16/NX-Shell/releases

Hell yeah there is bud! You've got a few options, you could use NX-Shell which is a file browser found here or can be found on the homebrew App Store, second you could use Hekate and put your system into USB mode then connect to the system with your computer via USB although it sounds like you want to avoid your PC so the first option may be best.

yes you can use FTP, either https://github.com/mtheall/ftpd or https://github.com/cathery/sys-ftpd-light, you still need to transfer your files prior, also you can mount your switch via usbc cable using tegragui, I also believe there's a homebrew app that allows you to access the microsd card via usb cable https://github.com/retronx-team/mtp-server-nx i think