The firmware of this GPON ONT SFP module can be updated using the web interface (Management | Update Software):
The web interface only accepts image files with a special header. These can be created by adding the header to a flash dump.
This example setup for RouterOS 7.22 configures a MikroTik router as a PPPoE offloader. The router establishes a connection to a PPPoE server (e. g. over GPON or DSL), acquires an IPv4 address and an IPv6 prefix and delegates these to a downstream firewall via DHCP. The MikroTik device acts purely as a router, it has no firewall / NAT rules.
This is motivated by wanting a basic IP over Ethernet connection for the WAN interface of the main firewall (e. g. OPNsense). Specific hardware and protocols required for the WAN uplink are handled by the MikroTik device. RouterOS is known to have a robust PPPoE implementation.
It is assumed that the router has no default configuration like bridges, firewall rules etc.: