I see two separate issues:
Here is one recent instantnoodle thread: Easy installer läd e-latest-s-instantnoodle.zip (1.18 GB) fertig und sagt Versuche es nochmals - immer wieder
I am not sure why Easy Installer attempts to load OnePlus8/e-latest-s-instantnoodle.zip (notice Android 12 S) as … compare documentation and downloadable Android 11 (R) ROMs
which led you to prepare the device for Android 11 as you say here Oneplus 8 - Manual installation leads to a phone stuck in fastboot mode - #11 by thealpman.
The reason Easy Installer stopped may in fact be different; please read any of the recent Easy Installer or easy-installer tagged threads.
Notice many feature this sort of “Download fails” or “Try again” issue.
Maybe you can dig out the log file as Howto troubleshoot issues with the easy-installer.