Seal garage sanding

I want to seal the concrete floor of my new prefabricated garage (PU or epoxy). According to the prefabricated garage manufacturer, the floor must be ground beforehand (I think because of cement slurry).

Can I grind with an orbital sander? What grit sandpaper should I use? Or do I necessarily need a diamond grinding disc and an angle grinder? I want the floor to remain nice and smooth and only remove a very thin layer.

What would you recommend?

We also have a chemically resistant sealed floor at work, which is always roughened up with a parquet sander when repaired and then resealed. I suspect you don’t get much off by sanding. In our garage, however, the concrete was removed today with a milling machine, and the cement screed will be installed on Monday. Visually, it looks very smooth.

According to the prefabricated garage manufacturer, the floor must be sanded beforehand

Which manufacturer is your garage from? Have you sanded and sealed in the meantime?