FYI I was able to solve this by following the suggestions from a post about the same issue in another version of MacOS on Reddit.
To recap: Spotlight wasn't working and attempts to get it to reindex by adding and removing a folder from Spotlight Privacy in System Settings resulted in an error "Privacy List Error." In addition to this issue Finder would not display recent items, nor did any other app. Considered it a different issue but apparently not, because both have been fixed. And to give the developers at MacPaw some love, I removed CleanMyMac X completely and the problem was still present. I have never had a problem with CleanMyMac and I think it's a Mac essential, personally. I love it (I stand with Ukraine). Deleting my antivirus: also no effect. Reinstalling Sonoma: also no effect, strangely. Maybe one has to do a clean install not an installation-in-place. Anyhoo...
Here's the fix:
Boot into recovery mode and disable System Integrity Protection by opening the Terminal from the Utilities menu, and entering the following:
csrutil disable
Reboot (you can just type reboot into terminal and press Enter to accomplish this)
Login to your mac as an administrative user.
Open System Settings > Users & Groups
At the bottom, beside Network Account Server click the Edit... button then from the popup window click the Open Directory Utility... button.
In Directory Utility, click the lock icon at the bottom of the screen and enter your administrator password to unlock the settings.
In the Directory Utility main menu at the top of the screen, click Edit > Enable Root User and give it a password you will remember.
Close Directory Utility and System Preferences.
Open Terminal
Disable the Spotlight daemon by running
sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist
User your own password for sudo commands.
Disable Spotlight indexing by running
sudo mdutil -a -i off
Become the Root User by running
su
Enter the password you just made for the root user.
Delete the Spotlight index by running
rm -rf /System/Volumes/Data/.Spotlight-V100
Quit su by running
exit
Enable the Spotlight daemon by running
sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist
Enable Spotlight indexing by running
sudo mdutil -a -i on
Reindex all volumes by running
sudo mdutil -aE
Go back into Directory Utility and disable the root user from the same menu where you enabled it.
Wait for indexing to finish. For me it took about an hour. You can check it with Command+[space], the indexing status appears below search bar.
When indexing is complete, reboot into recovery mode, open Terminal and run the following to enable System Integrity Protection.
csrutil enable
Reboot. Spotlight and recent items in Finder should operate as expected once again.