How to fully back up a Tolino Vision Color + devmode update.tar stopped working

[Siren1305]

Hello there, I've recently bought a used Tolino Vision Color and was trying to flash Kobo software to it, because from what I understand, that gives you the best user experience. As the GitHub repo recommends in the very beginning, I wanted to start off by backing up the whole eMMC, but couldn't find anything on how to do that, except for one thread here that suggests dd'ing the device to an image file, which I don't think will work since the device doesn't make its whole storage visible to the computer it's connected to. I tried playing around with mtkclient to somehow gain access to the eMMC in the BROM phase, admittedly doing stuff that a hallucinating AI told me to do, but I kept getting "handshake failed" errors, and the Tolino factory reset itself twice while I was trying to get it to work. (Another interesting point, though I'm not sure if it's meaningful, is that My Notebooks went from being in the More tab to having its own tab a few times.)

Since I was getting nowhere, I decided to try accessing the storage via ssh and tried to install NickelMenu, but that failed too. Maybe it's because I should switch it to Kobo mode first? To do that, I copied the update.tar that's supposed to enable devmode, and the updating screen appeared when I safely removed the Tolino, but nothing changed after the reboot, not even after searching for the word devmodeon. However, it was working just fine before starting to try to backup. It looks like I somehow gave the thing immunity to the devmode update.tar file while playing with the mtkclient.

I use Fedora Linux, and the e-reader is on firmware version 5.15.245253. I have no prior experience with e-readers, much less with hacking them. Any help appreciated!

[Siren1305]

Update: I got the devmode working again! Turns out the tar file I was copying was corrupted. My question about how I should do the backup stands.