Downgrading the OS...restore apps from TimeMachine? So I’m downgrading the OS from Mojave to back to Lion..backed up hd with TimeMachine. I will erase the drive and install the older OS. My question is will I be able to restore my applications from my TM backup?
You will be able to restore everything from the backup which was done on the same or an older version of macOS Lion (10.7.5 was the latest, so if you just downloaded it from the App Store, you will probably have this one).

From later backups you have to copy/paste everything manually.

Also for Apple apps like Safari, iTunes, etc. only the latest version that was provided for the OS version your are about to install will be available, eventhough you haven't updated it to that version at the time of the backup.