WAN / Internet : : FTTH provider : .----+------------. | PPPoE Router | (or Bridge, whatever) '-----+-----------' | WAN | .-----+------. | OPNsense | '-----+------' | LAN
You should be able to get a fibre modem that would bridge to ethernet AND support VLAN. That's how my VDSL works now, the modem is in bridge mode but it's using VLAN101 to connect. Opnsense then just does the PPPoE as normal.