See in general the free courses are not that good as you expect. They are not covered well or the certificate will have a good value until and unless you do it from a reputed place. If you ask me then I would say if you want to invest time then you should invest in a full time course. These will add value to your CV and will help you to achieve your goal. Now if you have a basic degree done then go for companies like Upgrad or Coursera and do courses from there are well reputed companies and you may have value. Also you can do courses from government online courses like NPTEL which will also provide you certificate and it will be valid for your job purpose.

The main point is pursue a course from a proper institution and learn the course in a good curriculum wise. As you know its a applied field, you should find such a course that will help you to gain practical experiences.

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I hope my answer helps. All the very best for your future endeavors!