Hello, friend!
I just tried it. According to the error message in the problem description, the GPON configuration mode does not match.
You can run the display gpon global-config command to view the GPON ONT home gateway config method.
Generally, the GPON ONT home gateway can be configured and modified on the OLT only when the configuration method of the GPON ONT home gateway is OMCI.

If the GPON ONT home gateway config method displayed in the command output is not OMCI, you need to run the gpon ont home-gateway config-method omci command to modify the ONT, and then try to reconfigure the ONT.
Thanks!