How can I dump all the stock partitions before rooting?

The phone in question is a Moto g8 Power (XT2041-3; sofiar). The bootloader is unlocked, but I was not able to find any custom recovery for it – just a lot of dead Google Drive links on XDA. From what I've gathered, since the phone shipped with Android 10, it should be possible to just boot a rooted GSI and dd the partitions from there (I'm proficient with normal Linux, so that shouldn't be a problem).

At first, I was looking for a right KernelSU image, but none of the artifacts included in their GitHub releases seemed to use an old-enough kernel version. Am I missing something?

Now I've also found this guide, which seems to suggest I could just use a userdebug GSI directly from Google. But trying to download any of those Android 10 aosp_arm64-img-*.zip files straight-up fails with a cryptic error message.