You can’t format or mess with a drive you’re currently using.

Grab a USB flash drive, plug it into your Deck and download https://etcher.balena.io/ (select AppImage) and https://neon.kde.org/download (user edition, on the left).

Launch Balena Etcher. Press’ Flash from file’, select the ISO file neon-user-xxxxxx.iso you downloaded, Next select the USB drive you plugged in. Press ‘Flash’. Wait for it to finish.

Reboot your Steam Deck and enter the boot menu. Select the USB drive you just made. Wait for everything to load (be patient) and then a window should come up asking you to ‘Try’ or ‘Install’. DO NOT PRESS INSTALL, press ‘Try’.

You should now see a screen that looks just like SteamOS Desktop, but it’s actually running off of the USB and thus you should be able to resize the partition.

Maybe poor choice of words on my part. I was referring more to mDNS being vulnerable to impersonation and MITM attacks as what’s unsafe, not using .local in and of itself.

Is SSH actually running on port 22? Check /etc/ssh/sshd_config.

Consider also enabling and trying to SSH into your Windows PC. If that also doesn’t work, then most likely your router is set up to block SSH by default.

Possibly this? https://github.com/systemd/systemd/issues/28983#issuecomment-1697260469

The .local TLD is considered unsafe anyway, so personally I’d recommend editing /etc/hosts instead.