Work task in the application process?

Hello, my dears!

I'm currently in the middle of a long application process and have been invited to numerous interviews. After a pleasant initial interview, I'm usually sent sample assignments. These are usually very extensive and take up to 3-4 hours to complete. I'm slowly finding it very frustrating to do unpaid work, especially when I'm still rejected.

Question: Is it really common practice to always put in so much effort during the application process? Do I have the right to decline and ask the employer for alternatives?

I'd be interested to know.

Thanks!