Congratulations on the new release! 
From the side of conda-forge, I also have some good news: for the first time, we’ve managed to start the migration for the new python version based on the release candidates (though we’ve been wanting to do that for a long time…), and I’m happy to say that we have launch-day availability of over 1000 packages. 
There are – unsurprisingly – some notable exceptions, e.g. where the respective upstream libraries are not yet 3.12-compatible, or more complicated cases like scipy (due to outsized impact of the distutils removal there). In each such case this means that all dependent libraries also have to wait until the respective builds get unblocked.
We track the status of all this here, and people are welcome to help unblock key packages (either in conda-forge or better: directly upstream). We’ll be keeping up the pace to unblock more packages as soon as dependencies, automation & review allow. 
In any case, you should already be able to do:
mamba create -n my_new_env python=3.12 pandas requests pillow # and many more
Happy coding with Python 3.12!
PS. Huge thanks to @uwe for being the driving force behind this effort!
