Can anyone suggest some interesting backend projects ??

Role based authentication is good for beginners.

Found this on google.
gist.github.com/MWins/41c6fec2122d...

The Curios moon. A novel and a training guide to massive data analysis in Postgress. You will need a large hard drive though as the datasets can run to several gigs.Space produces a lot of information!

Things I keep meaning to build:
Typing speed assessor
Poker tournament management app
Squash league / ladder app
Fantasy F1 game.

Currently learning React by building a cricket scoring app

Supabase?

Building an online multiplayer game can be fun. Other than that, you can build clones of popular sites (chats, forums, etc).

Join on our OSS Project SleekwareDB

Deno?

Check Thin Backend :)