@Myasu.1 "is my understanding correct that the above manual for Nucleo-L4R5ZI ?"
Just to be clear on the distinction between the board and the chip:
As the title says, That document is the Reference Manual (the Datasheet is a separate document) for the STM32L4+ Series MCUs
It applies to the MCUs themselves; it makes no difference what board the chips are mounted on - that is entirely outside the scope of that document.
However, the MCU mounted on a Nucleo-L4R5ZI board is an STM32L4+ Series MCUs - so this is, indeed, the relevant manual.
When your question is resolved, please mark the solution:

A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.