I can't install Unreal Datasmith exporter for 3ds MAX 4.26

Hello khitsk21267,

Yes providing log could be useful. The message shows that the installer is looking for a 4.24 version of the plugin installer. The only reason would be that it needs it to uninstall that version prior to install the 4.26.2.
I will check with the team if that is the expected behaviour.

Did you try to uninstall the datasmith plugin from windows> Add or Remove programs?

Bests,
Flavien.