unable to detach references

Why Not Do A Save As with a Different name. On the bottom right options. Select omit External References. When you open the newly named DGN the reference will be gone? 

We don't just Save As because more often than not, we have a designated design drawing that we are not allowed to create "versions" of, or to replace. We need to use this specific design drawing.

The workaround is to open the drawing with the appropriate design software and detach the file. Unfortunately, this is only a workaround, and not a fix. I can appreciate that certain changes to design drawings should be discouraged, but it is a a source of frustration and wasted time to not allow those changes at all.

I'm experiencing the same problems, only using ORD 2021 R1.  I have a survey file, when I attach and alignment file it will not detach.

Has a solution been found other than the save as?

Try selecting the 2d and 3d model attachments of that dgn and detach at the same time

Try selecting the 2d and 3d model attachments of that dgn and detach at the same time