Shut down your device, don't leave it on at all times. I don't know if there's a way to suspend and encrypt RAM though. But other than that, there's no way to keep a computer running without the miscellaneous data being kept in RAM
Besides memory encryption (AMD PRO & Epyc) you can zero-out in-use memory keys before suspend & restore on resume, preferably using sealed storage, like TPM. This is ‘the’ reason to prefer home encryption vs. full disk. The thing is if someone is prepared to attack your laptop with liquid nitrogen they might as well just wait for you to unlock your laptop and then steal it right there, or watch you type in your password; better get your privacy blanket ready ;) Not having physical security is a huge disadvantage, and there’s really no way around it—you automatically start in the defeated position, and have to stack gizmos just to break even.