Xiao Li-Po Battery Input - Tx Pin6 Voltage @ 4V but need 3.3V

I am having some voltage issues that I am trying to wrap my brain around…
Attaching schematic for reference.

Project overview - Communicating XIAO to DFPlayer Mini over serial to play music on the speaker.

When the XIAO is connected to the PC, the project works good. While connected to PC, I measure with my voltmeter on pin6 i.e. Tx pin and I get 3.3V and 5V pin has 5V.
When I disconnect the XIAO from PC and connect it to Li-Po battery which is fully charged, the battery output is 4.04V. When I connect Li-Po to 3V3 pin on XIAO and measure on the pin6 (i.e. Tx pin) I get 4.04V, same as battery. When I measure on 5V pin on XIAO I get the same 4.04V

DFPlayer mini needs to see 3.3V otherwise it may fry the board hence I was concerned putting 4.04V on the DFPlayer mini from Pin6 (Tx pin) on XIAO to Pin2 (Rx pin) on DFPlayer mini.

I have a logic level converter but it will not turn ON as I do not have 5V when connected to Li-Po battery.

Any suggestions on how to handle this? Thank you.