My biggest issue is the device not even installing Lineage. I'm not sure why. Would it have anything to do with using the latest Miui firmware? Because that's the only thing I can think of that I did differently here.
Edit: After the device reverts back to it's base Miui when trying to install a rom (while deleting twrp...)... I once again reinstalled TWRP, but then rebooted to see what would happen. Now it's stuck on the black loading screen with the "Mi" name in the middle... So could it be an issue with TWRP, somehow? :/ I'm using the latest gemini version...
Further Edit: It looks like it all had to do with installing the latest firmware. If I did the wipe, installed firmware, then lineage, it would crash then boot to Miui. If I installed firmware, booted normally, then went back to TWRP to do the Lineage install it seemed to work (on setup now. Hopefully all is good)
FURTHER further Edit: Root check finds my device isn't rooted. I did install the recommended addonsu with everything else, but apparently that didn't do anything. What am I missing now? :/