problem building 2.9.2 RIP

I have a 2.9.0~pre1 installed and running on ubuntu 22.04 with the 5.15.0-1061 PREEMT_RT kernel.
I am trying to build 2.9.2 before adding to my python modules and qtvcp screens. However, after
making a copy of the 2.9.2 git branch I can't get it to compile with:
> cd src
> ./autogen.sh
> ./configure
> make -j4
Makefile:121: *** Makefile.inc must specify RTPREFIX and other variables. Stop.

I check the debian dependencies and don't find any missing.
can't find any --rip options for ./configure
How are RTPREFIX and other variable supposed to get set?
Any help will be appreciated.

Forgot to add I want a RIP installation.
My 2.9.0~pre1 I'm using now has files added to share/qtvcp/screens. Is there a better place to add these and have linuxcnc find them?

I tried ./configure --with-realtime=uspace but autogen.sh complains about missing src/m4 files. I tried copying the m4 files it complained about from the 2.9.0~pre1 RIP installation but
gives errors about possibly undefined macros. Maybe there is a different git branch than 2.9 which is more complete?

I don't think anything has changed since I made this guide. I have certainl compile linuxcnc recently (for the 2.9 release)

Thanks, I'll work through this to see if I missed a step. But first I'll make a disk image so I can be sure of recovering the 2.9.0~pre1 install if something goes wrong and any new packages kill the old installation

Thank you rodw. I now have 2.9.2 installed and working. I just have to get to use my qtvcp and python code. It seems like there should be path variables I could set to put my additions into my config folder and not have to touch the RIP folder. Any idea how to do this?

give or take a typo (leading dot is important!)