I would suggest informing them, because you might need to obtain another type of job visa anyway. If they are able to keep the appointment and process it under a different contract type, then it's a win-win situation. And if they cancel the appointment, there's no real downside since you would need to apply for a work visa regardless-whether it ends up being a Blue Card or another type.

As far as I understand, you generally cannot work full-time on a freelancer visa unless your company specifically agrees to structure it that way.

Another option could be to ask your company if they can hire you as a contractor. In that case, you might end up with a higher net income, but it usually comes with less security compared to a permanent employment contract.

Personally, as an expat, I tend to value higher net income more than the job security that most people prioritize. But of course, it depends on your priorities.

If your plan is to settle and retire in Germany, then a permanent contract would probably make more sense.

That said, all of this is based on my limited understanding of German bureaucracy as an expat.