After the recent Acrobat update to version 26.1, I can no longer move or nest bookmarks.

You may want to switch from the “New Acrobat” interface to the “Old Acrobat” one to get better results. Use the View>Disable new Acrobat menu command to reboot into the older interface and try changing your bookmarks there. I think you’ll find you get much better results.

Adobe hasn’t so much changed how Acrobat operates as it’s distributed new features into “New Acrobat” and left the older ones in the “Old Acrobat” interface. I’ve been teaching my students how to quickly switch between the New and Old interfaces if they find Acrobat isn’t responding the way they expect it to.

In many cases, including this one you describe, it’s not that Acrobat doesn’t work the way it used to, only that the “New Acrobat” interface doesn’t. Switching back to the older interface compels Acrobat to work in many ways like it used to.

Hope this helps,

Randy