The time between pressing the alt-key and releasing it hat significantly changed in the latest version!
You now have to press it way longer! If you are used to the older versions you tend to release the key earlier und the process of duplication is not finished. This is with duplication of artboard the same as with alt-drag duplicating artwork. In the latter case I have even lost data because I worked with what I thought was a duplicate only to learn the the original was not duplicated beforehand.
PLEASE ADOBE CHANGE THAT BACK!
I can't notice any difference.
Which means what? That it is not true what I am saying or maybe that you pressed longer in the past and do not notice any difference?
I'm releasing the Alt key immediately.
Since it works for me it's not a general failure, but something related to your configuration.
Did you reset the preferences after updating?
Do you reboot the system regularly?
Does it work with a different mouse?
Collegues of mine have the same problem.
I do not see the problem. it may be related to GPU rendering.
Is it faster when you turn off: Preferences > Performance > Real-Time Drawing and Editing ?
Yes, that seems to help! On a short test the performance is way better and alt+drag-copying feels like I am used to.
Good to hear that seems to help.
But you will miss the Real-Time Drawing and Editing (but you have missed that already during the past 33 years).