Hello there,
For any B.Tech course, physics, chemistry and mathematics (PCM) are the compulsory subjects. The eligibility criteria doesn't mention about biology or computer science as compulsory subject, so you can choose any of them.

Now, if you choose biology, you can appear for medical entrance exams as well. Engineering, architecture, medical, and pharmacy - you can choose any path. For medical, PCB is compulsory, and for engineering PCM is compulsory.

While, if you choose computer science, you can apply for only engineering and architecture. You can give all entrance tests related to engineering and architecture, only.

And for Biotechnology, you don't need computer science background, but if you have knowledge in biology, there won't be much problem in understanding during your course, because you know the basics.

But, in 11th and 12th standard, computer science is easier to study than biology.

Now it's totally upto you what to choose. Whichever subject you choose, choose wisely. If your only aim is to get Biotech in IIT, then you need to get below 20k rank in JEE Main and Advanced.

Hope this answer helps you.
Good luck!!