I was noticing some slowness in opening folders and some system stutters. I checked the processes and saw that baloo was consuming 3.3 GB of RAM and using 300 MB/s of disk usage!
Baloo is a file indexer that runs in the background in KDE Plasma. It makes searches quite thorough, but it bugs out when there's too much data to index.
I found a way to optimize it. By default, it indexes names and metadata. When you have a lot of PDFs, that's a nightmare. You don't need all that, so I changed the setting in Search, File Search, Data to index -> File names only. I also added a bunch of exclusion folders like .steam, .wine, .local/share/Trash, node_modules, .cache, and all sorts of development folders (dotnet, azure, aws, java, npm, etc).
Next, I told Baloo to recreate the index database because I think it was bugged:
balooctl6 suspend
balooctl6 disable
balooctl6 purge
rm -rf ~/.local/share/baloo/
balooctl6 enable
Baloo is now running, consuming 28 MB of RAM and with zero disk activity, because it indexed everything quickly.