How to add downloads back to dock?

Thats hard to believe, Downloads is baked into the macOS.

Finder >Go>Downloads

option command L opens the Downloads folder.

What you want is open your Home folder, there will be you your Downloads folder in the list.

If it is not in the sidebar you can drag it there as well.

You can easily drag your downloads folder back to the Dock from your Home folder in the Finder; drag and drop far-right side of Dock.

Do you have you sidebar showing in Finder>View >Show sidebar

Finder>Preferences>Sidebar check the boxes

Get to know the Finder on your Mac - Apple Support

See and organize your files in the Finder on Mac - Apple Support

The home folder will have your account name, not "home".

What is in the Sidebar tab of Finder preferences?