roll back to a previous update xt1768

[doingthelordswork]

For some reason I can't flash Magisk on the latest updates (November / December) getting "unable to mount /data" or "unable to mount /cache" errors in twrp (3.2.3-r1) so I wanted to roll back to one of the previous updates (July / August) and try flashing Magisk from there. However, every time upon starting the flashfile I get this error:

Writing 'partition'                                (bootloader) Validating 'gpt.default.xml'
(bootloader) Security version downgrade
(bootloader) Image primary_gpt failed validation
(bootloader) Preflash validation failed
(bootloader) Cancelling 'gpt.default.xml'
FAILED (remote: '')

So I have two questions: 1) Was there something about the latest updates that prevents Magisk/root, and if so, how could I go about getting it done? Has anyone else run into this? I've read something about patching the boot.img, but I'm not sure what that has to do with this or how to accomplish that. 2) If there indeed was something in the recent updates that breaks the rooting process, is there a way to downgrade to an earlier update and get root from there?

Edit: rooted the phone by flashing a boot image that I patched through Magisk Manage. Didn't even know that's possible, as I used to always flash no-verity (as well as Magisk) through twrp on this phone.