Two things to try.
1. Let it sit on that scrolling line for about 3 hours. (Google doesn't give you the "Setting up 1 of ... apps" thing that Samsung did. But that's kind of what it's doing.)
2. If that still doesn't restart it, hold the power button in for about 30 seconds (it'll restart over and over - just hold it in until it vibrates. If it doesn't, go to the next and final step.)
Final step, if all else fails: Factory reset. If it's set to back up apps, it will start reloading them once you set it up (which could take an hour or two to complete, but that's computer time, not operator time - you can watch TV while it syncs). I'd suggest that, before you let it do that, though, you install TWRP (which means unlocking the bootloader, which means wiping the phone again - as you unlock it, it wipes). From then on, before you let it update, do a TWRP backup and copy the backup folder to a PC. Then, if you do have to do a factory reset, you have the entire user space (except /emulated/0, or "sdcard", which you can back up separately or, if there's enough empty storage, use
Tipatch on TWRP to back that up too) backed up, so a factory reset is just a little annoyance.
Oh, and if the bootloader is unlocked ... you can boot to the bootloader and fastboot boot.img (which you can grab from the latest factory image at
Google | Factory Images for Nexus and Pixel Devices) - I've "recovered" my P2 a few times with that. If that gets it back fastboot flash boot.img. (If boot.img gets corrupted, the phone won't boot.) Of course, since that may wipe TWRP, you'd have to reinstall it, but that's not even a minor annoyance - boot the TWRP img file, then use TWRP to install the TWRP zip file. (And install Magisk if you want the phone rooted for any reason. Just download the zip and install it from TWRP.)
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