Which apps do you use for reading programming books?

[AstonJ]

Ok just found it! You have to set it up manually:

How to sync Apple Books from Mac to iPad

Just writing this up in case it helps anyone else because it wasn’t automatic. First, connect you iPad to your Mac via a cable. On your Mac open a finder window and on the left hand side click on your iPad under Locations Click on the Books tab and then Sync books onto.. and All books Click on General tab and under Options click Show this iPad when on Wi-Fi and Automatically sync when this iPad is connected