Hi, sorry for the delay, I was confused, where is my response and today I found that there is second page to my post :-).
Answer to pdurrant, the directory selection is simple (I hope), it works like this
1. You have got books saved (in my case) in icloud folder called Books
https://postimg.cc/1fqL7VZs
2. When you open the app, you see there are no books yet and you have to select the folder, where books are
https://postimg.cc/nCBPG8vs
3. So you select that folder in the justRead app
https://postimg.cc/14NCyx70
4. It processed the files and you have the books in the app
https://postimg.cc/ZvrxpSXf
5. If you change something in that folder (for example change cover using calibre), you just refresh the library by standard: pull down
My goal here was: at the first start of the app point to the directory with books and refresh when you want to.
I managed to make it more performant than before, so 5000 books are analyze in about 15 seconds.