For a while I had fiber running through an XGS-PON SFP module in my own Fritz!Box. Now I use the provider's ONT (which is just a fiber <-> ethernet media converter) hooked up to a Unifi Cloud Gateway Max.
Plenty of folks here that have their UDM or OpnSense box hooked up directly to fiber with a Zaram XGS-PON module.
Also, I am sorry you have to deal with caps. Data has been unlimited here ever since we switched from 56k6 to ADSL. (I also have unlimited 5G for 25 Euro per month.)