I managed to resolve this issue, and I want to share the steps I took in case it helps someone else. Here’s what worked for me:
Optimize the Database
Go to Settings → Troubleshooting → Optimize Database.
If it doesn’t work (like in my case, where the server froze for 15 minutes), close Plex Media Server completely.
Use PlexDBRepair
Download the PlexDBRepair tool from GitHub (just Google “PlexDBRepair”).
It includes a batch script for Windows and a shell script for macOS/Linux.
I ran the script on my Windows machine, where my Plex server is hosted.
Restart Plex Media Server
After running PlexDBRepair, relaunch Plex.
In my case, everything worked perfectly, searching by original titles was functional again, and optimizing the database completed in less than a second.
If you’re facing similar issues, give these steps a try. They might just save you the headache I went through:)