Async DR vs Backup

Good morning... evening... night all over the world ^^

I'm wondering what are the technical differences between Async DR and Backup.

What I've red in documentation is that Backup does not allow running the virtual machines on the remote site.

This comes with many questions as I couldn't find any detailed description of the backup mechanism.

As far as I understand, both works exactly the same. Only difference is that on the remote site, the backup target PD cannot be promoted to allow running of the VMs.

Is this correct ? is this the only difference ?

Otherwise, what are all the differences between both modes ? Any impact on the size of used on the target space ? ...