Part of macOS
mdworker_sharedSpotlight indexer
○ Leave it
Reads new and changed files so Spotlight search can find them.
What it is
Short-lived workers that open files and pass their contents to Spotlight. Several often run at once.
Why it might be busy
After a macOS update or after copying many files. Usually 10 to 30 minutes, longer after an update.
If you stop it
macOS starts it again straight away. Leave it.
The verdict
○ Leave it. Part of macOS, or something that starts again by itself. You never need to close these.
In Activity Monitor
mdworker_sharedmdworker
From Procession’s guide, in the words the app shows.