Spotlight won't index any of the standard built-in macOS apps. It *does* index all the 3rd-party apps. Any suggestions? This is on a 2019 MBP running Catalina 10.15.7. I also have a 2012 Mac mini running the same OS, and that has no problems indexing all the apps.
I should point out that I've tried all of these:

Added the system drive to &quot;Privacy&quot; in Spotlight and then removed it
Revealed the hidden Spotlight folder and deleted it
Run sudo mdutil -Ea /

Nothing's worked. Where can I go from here?
To reiterate, it indexes all my third-party apps with no issues. It's only the built-in standard macOS apps that it's refusing to see.
Back in 2019 I had a client whose Spotlight wouldn't index fully. We ran Etre Check on his machine and got back some info from mds, reporting that mdimporter was crashing, and it gave us a file id.
I had him open up a terminal and put in sudo mdutil -t &lt;number&gt;. It came back with a path to an email. I had him open up that email (with open &lt;path&gt;), he reviewed the email, decided he didn't need it and deleted it.
IIRC we had to repeat the process multiple times until mdimporter stopped choking on his files. Not sure what kind of bug we tripped, but after deleting maybe file of his files, his system indexed properly.
Start here and see if this shows anything related to Spotlight, mds, or mdimport.
Etre Check