In that case you should switch to the 6n138 now as trying to change it later will be a pain and may break routing. The 6n138 available in core parts doesn’t have pin 7 included and that is needed to implement the circuit shown here:
I can modify your current 6n137 part to be a proper 6n138 (with pin 7) fairly easily and add the suggested 74ls14 or 74hc14 fairly easily.
The pcb view on the part was broken (no holes generated in the gerber) and the labels in breadboard are misplaced leading us to short things together which tied 5V to din (which isn’t correct). I have a corrected version of the neo pixel and will swap it in and make sure the routing npw works correctly.
Peter