Hey @langesmalle,
The issue with deb that you’re hitting is a bug that we’ll be getting to soon. In the meantime, since you’re not using any deb content, we can do a workaround. Try running the foreman-installer with --katello-use-pulp-2-for-deb=false --katello-enable-deb=false and then redo content prepare. Then, you should be safe to do the switchover. You can turn Debian back on after you’re on Pulp 3 if you wish.
Related thread: Pulp3 Migration failed
That doesn’t sound right, is there any chance I could see the context?