Welcome to the forum!
It sounds like you're facing some challenges with finding gear that works with your Rivian R1T for overlanding purposes.
First off, you could go with a portable 12v battery pack that you can recharge separately and then use to power your winch or any other 12v gear. There are multiple options ranging from being small and compact to large and hulking ones.
Alternatively, you could install a separate 12v system solely to power your winch or any other equipment. But you'll have to get some additional wiring and possibly another battery. This decision will help you duck into the Rivian's internal 12v system. Lastly, pick a winch that consumes fewer amps than your Rivian's 12v system can handle. That way, you will avoid overloading the system and causing damage. It's best to go slow with modifying your vehicle and do enough research before implementing changes.
You could also talk to a professional mechanic or electrician familiar with EV systems and overlanding setups. Have a great time overlanding!
