Kannada cinema, also known as Chandanavana or Sandalwood ,is the Indian film industry based in the state of Karnataka where films are produced in Kannada.
Even though their is rapid growth in internet connectivity,Kannada industry has failed to strike a chord with audience due to lack of awareness about the streaming of movies online.
Popular sources to look out for Kannada movies
YouTube:-This video sharing website is the most used one across the globe. It is available by default for android users . Most of the Kannada content is available free of cost.One can find many Kannada classics like Bangarada Manushya, Kasturi Nivasa etc along with a finite number of new movies like Shravani Subrahmanya, Doddamane Huduga etc on YouTube. Some of the important channels where you can watch Kannada movies are:-

Netflix:-This global giant also boasts of some of the most critically acclaimed movies like U-Turn, Thithi ,Rama Rama Re etc.But the number of movies available is very less when compared to its competitors.

Amazon Prime video:-It is owned and operated by retail giant Amazon Inc.A lot of benefit is available if you subscribe to it. You can find blockbusters like KGF ,Kavaludaari etc on it.

Hotstar:-It is an Indian based streaming platform which is operated by Star India,which in turn is run by Walt Disney.You can find movies like Mungaru Male,Duniya ,Maankiya,Aa Karala Raatri etc which has been screened on Star Suvarna.
https://www.hotstar.com/languages/kannada

Voot:-It is owned by Viacom 18.Here,you can find movies which has been aired on Colors Kannada ,Colors Super and Colors Kannada Cinema.Some of the prominent movies available are Gultoo, Operation Alamelamma ,Kirik Party etc

Zee5:-It is operated by Essel group which owns Zee Entertainment Enterprises Limited .Some of the prominent movies are Milana, Natasarvabhowma, Hebbuli etc which has been aired on Zee Kannada.

Sun NXT:-It is operated by Sun Network Limited which operates Udaya TV and its sister channels. Prominent movies available are Rajakumara , Aake, Kotigobba, Shankar Guru etc

Eros Now:- It is owned and controlled by Eros Digital, the digital media management arm of Eros International.It has a decent number of Kannada movies in its catalog.

Jio Cinema:-This app developed by Jio hosts a fair number of Kannada movies.
https://www.jiocinema.com/language/kannada/movies/all/0/9/0

As far as I know, these are the most prominent sources to watch/download Kannada movies.