How many skills can you learn at a time?

Fundamentally, when you say you have learnt a skill, you are doing some sort of activities.

How many skills can you learn when you are cooking?

How many skills can you learn when you are working on a coding project?

It just depends on the width of the activity. If your coding project require you to be end to end from planning a software to deploying and maintaining a software, then I would say plenty of skills that you can learn.

But there are tradeoffs. If you try to do every step by yourself in the short term, it is hard for to go deep into one skill. So someone may find that learning one skill at a time and learning it really well may be more useful in the real world situation.

Somebody want to go fast and understand the big picture. Somebody want to go slow and enjoy every piece of the tiny action. It just depends.