On this point, I recommend reading my post on what randomizing the routers MAC address will and won’t do. Its a relatively low-effort but low-yield outcome.
You can also buy your own Modem, but this gets trickier with fiber. Even so, the ISP needs to configure your modem to work with their setup.
PPPoE seems to be common for DSL from what I briefly read. For cable or fiber, don’t think this is an option. And I’m not sure why you’d recommend bridged mode - this is for specific topologies, not just every use case.