Should I do freelance of my skills on weekends or learn new things?

I've had several opportunities to do work as a side gig, and I can tell you that it is very difficult to do. Complex tasks as part-time work does not work well. I am not exactly sure why, it could be that humans only have so much bandwidth for problem solving.

We don't know enough about your circumstances to advise specifically but here are some of the factors I would consider.

Are you more concerned about short-term income or long-term earning potential? freelance if short-term income is priority.

Where are you at on your competence curve? If you are early the rate of learning and improvement is usually pretty steep. This means investing some time in learning will rapidly improve your skills. Once you are more mature in your core skills the curve usually flattens out and the value of each increment of learning is less.

How good are you with client/customer relations? Marketing and selling yourself? If those areas are currently lacking you should do freelancing as much for the opportunity to learn these people and business skills as for the the opportunity to make money. In the long run good customer service, negotiating and selling are master skills that will greatly enhance your career.

Why not both? The more side work you do, the more extra income you can earn. The more you learn, the more marketable skills you'll have to offer your clients?

I don't think it's an either/or proposition. I think it's a both/and...

This has proven to work very well for me.

I had a day job. I also had side work. One of my side customers asked me to come on with their org as a full-time employee. Instead, I started a company - and they are my biggest customer.

In my opinion learning new things will benefit in long run.