Mani Ratnam is one such director, whose movies are admired by more than three generations of people. For all the internet generation kids who want to watch all his films, here's a compilation of list all his films & where they're streaming. This list has been first compiled by a Twitter handle named, CinemaRare, famous for Sharing posters/stills/trivias/videos. And threads.
P.S: The list is in chronological order, from earliest to latest of his movies.
1. Pallavi Anupallavi, 1983 - Kannada
Available on YouTube
2. Unaru, 1984 - Malayalam
Available on YouTube
3. Pagal Nilavu, 1985 - Tamil
Available on YouTube
4. Idaya Kovil, 1985 - Tamil
Available on YouTube
5. Mouna Ragam, 1986 - Tamil
Available on YouTube
Mouna Ragam - Telugu Dubbed
Available on YouTube
6. Nayakan, 1987 - Tamil
Streaming on Amazon Prime: Link
Nayakudu - Telugu Dubbed
7. Agni Natchathiram, 1988 - Tamil
Streaming on YouTube, Eros Now & YuppTV
Gharshana - Telugu Dubbed
Available on YouTube
8. Geethanjali, 1989 - Telugu
Streaming on YouTube, JioCinema, Zee5, & Eros Now
9. Anjali, 1990 - Tamil
Available on YouTube
Anjali - Telugu Dubbed
Available on YouTube
10. Thalapathi, 1991 - Tamil
Streaming on Amazon Prime Video
Dalapathi - Telugu Dubbed
Streaming on YouTube & Amazon Prime Video
11. Roja, 1992 - Tamil
Available on YouTube
Roja - Telugu Dubbed
Available on YouTube & Amazon Prime Video
12. Thiruda Thiruda, 1993 - Tamil
Available on YouTube & Amazon Prime Video
Donga Donga - Telugu Dubbed
Available on YouTube
13. Bombay, 1995 - Tamil
Streaming on Amazon Prime Video Link
Bombay - Telugu Dubbed
Available on YouTube
14. Iruvar, 1997 - Tamil
Available on YouTube & Amazon Prime Video
Iddaru - Telugu Dubbed
Available on YouTube
15. Dil Se.., 1998 - Hindi

Streaming on Netflix Link
Dil Se (Prema Tho..) - Tamil & Telugu dubbed
Streaming on Amazon Prime Video Link
16. Alaipayuthey, 2000 - Tamil
Available on YouTube & Amazon Prime Video
Sakhi - Telugu Dubbed:
Available on YouTube
17. Kannathil Muthamittal, 2002 - Tamil
Available on YouTube & Amazon Prime Video
Amrutha - Telugu Dubbed
Available on YouTube
18. Ayitha Ezhuthu, Yuva - 2004
Tamil Version:
Hindi version available on YouTube & Netlfix
Yuva - Telugu Dubbed:
Available on YouTube
19. Guru, 2007 - Hindi
Streaming on YouTube & Netlfix
Guru - Tamil Dubbed
Available on YouTube
20. Raavan, Raavanan, Villain, 2010

Hindi Version:
Streaming on Hotstar, JioCinema & YuppTV Link
21. Kadal, 2013 - Tamil

Streaming on Hotstar Link
22. OK Kanmani, 2015 - Tamil

Streaming on Netflix & Hotstar Link
23. Kaatru Veliyidai, 2017 - Tamil

Available on YouTube
24. Chekka Chivantha Vaanam, 2018 - Tamil

Streaming on Hotstar Link
Tell us your favorite Mani Ratnam movie in comments below, And Which 'director's films on digital platforms' list should we do next, in the comments below.