I had to flash it in a very specific way, because with sp flash tool you need to have the auth file and the specific Download agent to write to this phone and I looked everywhere how to flash this thing and I couldn't make it flash any file in any way.
But then I discovered that the official Lenovo tool uses SPFlashTool to flash mediatek devices, so I messed around with it for a while and found out how to flash files to this phone
What I did was download the Lenovo MOTO Smart Assistant for Windows, went into the flash tab, selected rescue; then selected MOTO device, i chose my specific device model (which is Moto E6 Plus XT2025-1 4G/64G) and clicked in the download button to download the latest firmware.
After it finishes downloading, you can go into the software's downloaded tab, and in the bottom there's an option to open the default download directory. In there are all the files for rescuing the smartphone (Full ROM, Lenovo's provided spflashtool (which i guess is the one Lenovo MOTO Smart Assistant uses to flash this phone), Some Download Agents for SPFlashtool, and among other things).
So, what i did at this point is I closed the tool, got into the Firmware's folder, grabbed the Boot.img and modified it with Magisk's android app (there is no root needed if you don't intend to flash the file to the actual device) and afterwards, replaced the old boot.img in the tool's download folder with the new one generated by Magisk (of course, after renaming it to boot.img) and opened the tool again and went into the same tab, selected again my device, clicked in the rescue button instead of the download one, and followed instructions on screen. It seemed like everything went fine, but when I started the phone, bootloader stated that the system integrity was changed (because I wrote to flash that new boot.img) that's when i realised that the dm-verity is not disabled in boot.img on Oreo -> + devices, but at least i knew that we could flash files to the device.
At that point I tried everything to disable DM verity and other verification: Using kitchens (In windows and in Linux) , using python scripts, Manually searching where to disable it, but i couldn't get any software to correctly disable it and /or to unpack any of the img files of the Firmware (system.img and some others unpacked but i didn't find anything there) so if anyone can help with this it would be very appreciated.