Hello,
the FRITZ!Box 5690 Pro can be supplied with Internet behind a fibre optic modem of the Internet provider via WAN port, as described in this setup guide for the FRITZ!Box 5690 Pro:
https://fritz.com/service...If you have any further questions about the 5690 Pro, please do not hesitate to contact our technical support or purchase advice team by e-mail. Please send us the character string "#6996491" to the e-mail address: fritzhilft(at)avm(dot)de .
Kind regards from Berlin
Your FRITZ! team