I'm new to programming, I'm still learning in programming, sorry if my logic is not good,
if you don't mind if you can help me with what kind of code can solve my problem, so that I can learn to understand
Ok, now I understand.
It's ok that you don't know how to do something when you try to do it first time.
I have no experience with xamarin but in this case the problem is not with xamarin api.
You have read bytes from base64 it's ok.
Next you need to write them to the "disk" and then read them from disk as you did before.
So now you can google "how to generate temp name for file c#"