I was just able to add a Roamless eSIM on my Pixel 8 Pro, so the functionality in general is not broken.
I did it directly from the app, there was no need for a QR code. It took about 1-2 minutes of waiting on a screen that says to wait 2-3 minutes.
My setup is a little different than yours since it's the first eSIM I added. I have a physical SIM inserted as well, which was active throughout.
I was connected to the Internet through Wi-Fi while setting it up, not just mobile data. I read somewhere this was recommended.
Do you have Play Services installed? According the notifications, the app seems to be polling the Integrity API while attempting to add the eSIM. (Although if even the QR code didn't work, that's probably not it.)