I am about to send a custom Attiny841 dev board (aimed at Optiboot) to production and I thought, since I never used netiher this microcontroller nor the USB-UART converter before, I'd come here and ask for a quick review. Please note I have already looked online and there are very few schematics online based on the Attiny841 and the MCP2221, and none sufficiently close to this one for me to be certain of the schematic.
Finally, there might be some improvements to make.
The routing is not an issue, I am more concerned about the subtleties of the schematic.
(note my ICSP header does not have a "spiral around" numbering, and CTRL0/1 are FastLED digital outputs)