Q1.
1) Click "FT" on search bar
2) Click "Show indexing status button" which shows books indexed
3) Click "Index books in this library to allow searching their full text" to clear the checkbox
4) Click to confirm you want to do that.
Q2.
Just delete full-text-search.db from the calibre library folder (while calibre is not running). Source Kovid in this post
https://www.mobileread.com/forums//s...13&postcount=2