I downloaded LibreELEC 9.1.501 for the RPI4. I added my remote USB stick receiver and the Remote tevii_nec. But it did not recognize it. As i copied the tevii_nec to /storage/.config/rc_keymaps/tevii_nec_patched and changed the UNKNOWN in the header to NEC it worked.
could you explain it a bit better what you done ?
what hardware do you run ?