ASIO 2.3 is the latest version of SDK (-> https://www.steinberg.net/de/company/developer.html)
If you look into the RME handbooks and search for "ASIO 2."
I some handbook you will find references to it, in some not.
UFX+ is i.e. using ASIO 2.3.
In BBFP manual you see it will work with all ASIO 2.0 compatible programs.
In the RayDAT manual you do not find any reference, but as I have the card, you can see in the driver settings dialog its ASIO 2.3.
As RME will certainly use the latest and greatest ASIO verion for its interfaces I would guess that all support the latest version 2.3, as even the older cards use current drivers from download area.
If I were you I would simply choose an interface 1st and then consult handbook or ask.
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14