I'm not sure if that applies to Fiber connections. I had my own fun with a firmware update causing latency issues with ATT Fiber's gateways that was fixed several months later [1]. I was using the combo ONT + Router originally and had to switch to dedicated ONT.
I ended up extracting 802.1x certificates with this[2] or a similar tool and interfacing directly with the ONT using OPNSense [3]. I was so angry I filed an FTC complaint because I had to do this bypass to do my job (the latency was so bad).