Hi, Garry!
Retrospective
Unexpected power loss (improper shutdown) could lead to data loss which was in-memory only or partly in memory and as not dumped into permanent storage. Perhaps you are fixing that issues now.
Did you tried to switch to virtual terminal (TTY), for example TTY3: Ctrl+Alt+F3 and to try to see processes state there and if you would be able to stop update process and wait many minutes to let it to stop by itself, to proceed with gentle reboot by calling systemctl reboot?
For future try to prevent such shut down also by [HowTo] reboot / turn off your frozen computer: REISUB/REISUO
To the current state.
If you have backups (i.e. Timeshift snapshots) may be better to covers previous state of file system than to fix it.
I completely do not know details of your issue, but if I would not have backups I would try to resurrect all execution files first: pacman/Tips and tricks - ArchWiki
That will download about 2.5-3 GiB data from Internet.
Also may be better to rebuild all AUR packages which executable files was running at the moment of shutdown.
Unfortunately the suggestion will not fix possible corruption of user config files and user data files. Better to restore filesystem system state from a snapshot.
Also try to remember what user files (did you have opened / were in use) and try to check them for corruption (to compare byte-to-byte with their backup copies or at least visually).
For a small and several files the
~/Desktop ❯ pamac info kompare | grep -iE "name|desc|repo"
Name : kompare
Description : Graphical file differences tool
Repository : extra
tool could be used.
But I am not a master of restoration, I do not know how can I help you more.
Hope you will be able to fix results of the issue.
Cheers!