You are forcing the system to use no driver for the nvidia card when blacklisting nouveau unless you also have installed the nvidia drivers.
What I do is similar (but different)
I install using the troubleshooting – basic graphics path as you did.
I then, during first boot enable the 3rd party repos.
Once that is done I open a test terminal and install the nvidia drivers with
sudo dnf install akmod-nvidia xorg-x11-drv-nvidia-cuda
After that completes I wait about 5 minutes and reboot.
The nvidia drivers will now load, the nouveau drivers are blacklisted, and all is good in the video world.
The only caveat there is that the user has to disable secure boot or sign the nvidia modules before the system is able to load and use them.
I just did a new clean install of F38 on a desktop where I installed a new drive for the OS and this is the process I used.
When the screen is flickering as it does when nouveau does not properly support it and before the nvidia drivers are installed, one may simply add the ‘nomodeset’ line into the kernel command line during boot to force it out of modeset, and the nouveau drivers will function well enough to do basic tasks like the terminal window I noted while installing the nvidia drivers.
There have been several reports of problems caused by totally disabling loading of the drivers for the nvidia card in an optimus configured laptop.
In fact, the nvidia card is not normally used when running apps in fedora/gnome unless the user selects to use the dedicated video card when launching app.