What category does learning robotics on my own go under UCAS Extracurricular?

Hello I think the title is quite self descriptive. I am an engineering student and I learn arduino programming and robotics through YouTube videos and pre made practice kit that you can buy to familiarise with coding and PLC programming. What should I select as type of activity:

- Online
- Skills and attainment raising activity
- Other

I am mainly doubting between online or other but is also a skill raising activity so I am not sure

If you mean the 'other activities' section on UCAS, then neither. That section is for outreach programs that universities and other organisations run.

This would be best suited for your personal statement, where you can also talk about what you gained from doing those things.