1-Pack 10G Converter: RJ45 Cu UTP to SFP+ (10G/5G/2.5G/1G/100M) | 10G/5G/2.5G/1G/100M, auto-negotiation, RJ45 to SFP+, plug-and-play, metal case, LFP,jumbo frame,10km,low latency,full duplex!

Something like https://www.amazon.com/dp/B0FC5K95KG/ would accept RJ45 from the ONT, convert it to SFP+ so you could run it over the fiber, then the SFP at the other end could plug into the UCG Fiber. I'm not sure about UniFi, but some brands do lock you into their own branded SFPs, so check on that before you buy generic ones. The UCG Fiber does have 10GbE WAN, so this is a lot of extra stuff just to hide the cable run. If there's any way you can manage to run Cat6, it's just a simple matter of plugging in each device at the end. Depending on the incoming fiber/ONT setup, you might be able to simply adapt the incoming fiber to the G.657.A2 fiber with a coupler and put the ONT in the same location as the router. Then you're just using a better-looking fiber run and avoiding all the copper-fiber conversion stuff.