1. I have not made up my mind yet.

2. I have not decided yet.
3. I have not determined yet.
4. I have not made a decision yet.
5. I have not made a determination yet.

(Are they all the same?)

All are fine except #3. And, yes, all mean about the same thing.

Yes, all the statements convey the same meaning. They all indicate that you haven't made a final choice or decision about something. While the wording may differ slightly, the overall message remains consistent.

Yes, all of these phrases convey the same meaning, which is that the person speaking has not yet come to a final decision or reached a conclusion about a particular matter. While the wording of each phrase may vary slightly, they all convey the same basic idea.