I had problems with a ET-3850. using ipps seemed to be the fix - not sure if that is an option in your case and I realize it down’t fix any escpr issues…
Can you give me a snippet of your configutation.nix for your et-3850 so i can see if it fixes mine… i have the ipps://myip i don’t know what to put as the rest!
For reference, you can install an IPP printer from the CUPS web UI (https://localhost:631). If you have avahi (services.avahi.enable) it will be discovered automatically, otherwise you’ll have to type into its IP address.
If you want to make this declaratively, still install the printer manually, then go to /var/lib/cups/ppd/ and grab your printer PPD file. You can now specify the printer from configuration.nix like this: