The PBN endorsement to an IR became required for PBN airspace or approaches (defined as routes or procedures requiring RNAV or RNP capability) on 25th August 2018, with it becoming mandatory for all IR tests (both initial and recurrent) from 25th August 2020. It has therefore been a requirement for any airways flight for over a year - RNAV aircraft equipment became a mandatory requirement for airways flight some years previously, phased in at various altitudes/levels for different countries, but generally required for any airways operations across Europe since 2012. It did take some schools a while to catch up, certainly in the UK it wasn't long ago that even some very major schools were teaching students to track VOR to VOR rather than waypoint to waypoint using RNAV.