Best/preferred method to backup working sd card images?

What software or method of backing up working system images is suggested or preferred? I want to be able to try out different images without having to redo a base config for a working image.

We typically recommend using multiple MicroSD cards. But if that is cost prohibitive, you can backup the entire raw disk using Linux’s dd command.

Put the MicroSD card in another computer and use:
sudo dd if=/dev/BLOCK_DEVICE bs=1M status=progress | zstd > IMAGE.img.zst
Replace BLOCK_DEVICE with the device that the MicroSD card.

To restore:
zstdcat IMAGE.img.zst | sudo dd of=/dev/BLOCK_DEVICE bs=1M iflag=fullblock status=progress

You can give it a try to make sure the command works properly. It’s a little slow since it may have to back up the entire MicroSD card including empty space.

and what would the recommended solution be for windows?

You can use Win32DiskImager but it’s going to be a big file.