Youtrack is great but complicated with it's UX. Code level extensibility with Project management tools is near zero. We are working on our extensibility framework called Propel, it gives you the ability to write code with React to extend Plane. Open-sourcing in Q3 2023.

That's a bit unfair towards youtrack, you can extend its behaviour with arbitrary javascript. It's not the cleanest development experience I had but it is powerful.

Unless I'm misunderstanding what you mean by "code level extensibility".

Now this extensibility is what I’m interested in, as I’m working in a project which needs front end extensibility and have no idea where to start!

we are trying to work with ~35 volunteers for this purpose, but i will check it out nonetheless.