I had a feeling, that anything could happen to the server and nobody will have access to the files anymore.
I temporary reuploaded the following files on my download server, till the originals are back online:
Armbian_23.08.0-trunk_Rk3318-box_bookworm_edge_6.3.13_minimal.img.xz
multitool.img.xz
nvram_2734c.txt
Link:
https://dl.timfischbach.com/dlc/RK3318 Files Reupload/