I'm not a subject matter expert by any means, but the 8311 Community Firmware group has made great strides on their SFP+ ONT FWs. The majority of users are using their WAS-110 implementation for XGS-PON to ‘bypass’ the ISPs ONT/Gateway device, in the states there's a lot of users doing this on AT&T Fiber, but the Discord community has a large global following with users around the world reporting success. They have some users on GPON, its a bit of a different bypass but people have been successful. I run a bypass directly into my UDM-Pro using a WAS-110.

https://pon.wiki/guides/masquerade-as-the-att-inc-bgw320-500...

Discord: https://discord.gg/8311