Issue obtaining mending book

Hello,

I've recently created a new world on 1.20.2, upon creating some librarians and not finding mending I did some research, it appears there has been an update which you now a jungle villager to do this.

I created a village in a swamp and obtained multiple jungle villagers which are now master librarians but still no mending. I thought this may be to do with R&G so placed a lectern what felt like several hundred times and still no mending.

Have a missed something obvious or are there other people struggling with this issue?

Many thanks

Jianneo