I am not sure if this is correct.
I feel that from the beginning implies something that lasts until now, while in the beginning implies something that only existed at the beginning. Please correct me if I am wrong.
OP is correct.
Except that "from the beginning" is not necessarily "until now." It could just mean from the beginning until a stated end, like:
"from the beginning of the Roman empire until the end of the Roman empire..."
But yes, "in the beginning" is a point in time, (a.k.a. the beginning).
"From the beginning" is a period of time (though not necessarily until now), determined by the use of until (stated end).
Yes, OP is correct. "From the beginning" implies something which lasts until now, while "in the beginning" implies something which existed in the beginning only.
Let me supplement this with an example:
Hope the issue is clear now.