You can flash Magisk from recovery if there's an "install from zip file" or something similar.
Or you can unlock the bootloader, but that voids the warranty. (Or you can go with a Pixel - Google doesn't seem to care if you root the phone, unless you did something with root that caused damage).
There's an XDA thread on getting it rooted - they haven't yet.
Or this, if you're a little bit technically inclined (use your own boot image file, though).