afni.nimh.nih.gov

The "detached from terminal" is normal behavior, but it appears you have not set the DISPLAY variable, and you may not have installed an Xserver too. The installation for WSL under Windows requires a bit more than native Ubuntu:

[afni.nimh.nih.gov]

WSL version 1 is easier to configure than WSL2. You will also need to select an Xserver (VcXsrv is the one described in the instructions).