NX-Shell VS ftpd

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.

you can interact with your SD card without taking it out using FTPD

Run sys-ftpd or ftpd and access your files from a computer using an FTP client

Use FTPD for quick file transfers to the 3DS over wifi without the need of removing the SD card. Available in the Universal Updater app.

FTPD: https://github.com/mtheall/ftpd/releases

I don’t have what you’re looking for but I have a solution for your screwdriver problem. Here is a video explaining how it works.

I have ftpd on my 3ds and I use FTPCafe FTP Client on my Android phone, then i download DS roms on my phone, after this I share internet (hotspot) to my 3DS, start ftpd on it, then put the IP that it says on the phone.