@anghela148 According to Immitracker, there have been Developer Programmers who have been granted visas under 189, so you can definitely try that. If you're worried about job opportunities, I suggest you look through job hunting sites like Seek Australia, Indeed, Jora, etc. and check for openings applicable to your field, and see if your skillset would fit most of the job openings.
Diploma/certificate is definitely cheaper, but you'll have to check if their curriculum fits what you really want to learn. Because some universities have unique courses/units that are only available there and not offered by VET schools. Since you already have a bachelor degree, you can look through masters programs, which can take as long as diploma courses (2 years). Of course, the downside is that they will cost you twice as much (around AUD 15k per sem).
If you will go straight for GSM (general skilled migration), you can definitely do so but you might need a lot of points to get an invitation right away (maybe 70+). With your 2 year work experience, you won't get any points for overseas work experience because the minimum is 3 years (excluding the year you are "unskilled," usually the first year you work). The student path is advisable only if you can afford it and/or if there are no other ways for you to claim points and increase your EOI points.