I can add value to RE by adding a bathroom, renovating the kitchen, ADU, etc.

In my early days of rehabbing I used to wonder how the heck do people miss-fire and pee all over bathroom floors.

Consider looking for a large single-family home with the ability to add more rooms or bathrooms, then rent it out by the room. 

Is it directly below a bathroom?

There were wet clothes in the bathroom floor and clothes and dirty dishes and rotting food all over the place. 

Every time they smoked in their bathroom, they would turn on the vent to get the smoke out which in turn made my whole apartment smell like a ganja lab.

Finished basement as well with additional room (and has the additional bathroom). 

You might want to consider adding another bathroom if possible. 

Quote from @Aditya Kohli: @Hamidou Keita I would recommend if duplexes are limited if you can get a 4-5 bedroom house and either rent by room for house hack or splitting a big house into 2 and adding a kitchenette and separate entrance as a more cost effective ROI option  It would have to be a house with 2 or more bathrooms.

Pic 12 (bathroom) has no vanity, just a floating sink.