@sarutobi1
It doesn't make sense to diasable and enable single interrupt flags inside an ISR. The hardware globally disables all interrupt when entering an ISR and globally enables, when leaving the ISR.
The UDRE flag is used to indicate, that the transmit buffer is empty. As you do not send anything, it will remain empty.
For what you described you will need to use the URXC interrupt, as in your first code.
Are you sure that there is no noise or any transfer on the RX Pin?
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