As someone who hires junior developers in a field that does not see much interest in the general hiring pool, I can assure you that having development experience from a previous job is better than having none.
If you want to go into ML or data science, you need to know how to program. It doesn't matter (in my opinion based on observation) so much what language. There is a small likelihood for companies to find graduates for junior roles that know the technology stack required in that field anyway.
If you were to apply for a role as, say, an Android mobile developer, and you would compete with someone with a computer science degree and half a year working as a Java developer, it might be a bit harder. In that case you would have to prove your soft skills are better, you have the ability to learn and pick up things and that in general you might make a better programmer than the other candidates.
However, since you want to go into a field where most people haven't got the exact degree for it (and degrees don't mean the world in software development anyway), I wouldn't worry too much. Your previous job proves that you can work. That you can learn a language. That you know how to write code. Now all you need to do is prove to them that you can also pick up a different technology stack.
If it was three or four years of experience in a language that is unrelated things would be a bit different. You'd have to convince companies that you really want to switch, that you are generally interested in this other technology. They might fear that you will be frustrated because your proficiency with that other language is way lower than with your .NET languages. That you might complain a lot and lower team morale that way. That you might suggest or simply go ahead and build tools in the language you know well. You would have to fight these prejudices.
But you're not in that situation. So, go for it! Don't worry about the half a year. It's actually a positive thing on your CV.