If i started brand new and wanted to become a functional Business Central consultant i would start with Erik Hougaards book. If you buy the digital version of the book you get access to updates of the book when new version of Business Central are released.
https://www.hougaard.com/book/
Then Microsoft learn
docs.microsoft.com/.../business-central
There is also a lot of information on doc
docs.microsoft.com/.../
The most important thing is to train yourself by using the software.
And make a list of what modules you want to learn in in what order.
Make sure not to just read about it. Get a sandbox, create your own company in it and then go through the modules in your prioritized order.
My order would be:
Financial management
Sales
Purchase
Warehouse
Power Automate
Power BI
.......and build from there.
I would also try to get a mentor so you have someone to ask and discuss aspects of the software with.
