cd4050 tx arduino at 5v converting to 3.3v by cd4050
Don't see how that would work.
If you power the 4050 from 5volt, it will still output 5volt logic.
And if you power the 4050 from 3.3volt, you could blow the inputs of the 4050 with Uno's 5volt logic.
RX/TX level shifter with 2N2222 here (not tried that myself, never needed it).