It looks like per this that the RAM can be upgraded in theory, but it would require replacing a sauntered chip on the motherboard, which requires specialized skill and tools. [br]
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It appears to be possible, but due to the difficulty, equipment requirement, and ability to easily kill a working board and chip - I wouldn't personally recommend it unless you are or are working with a specialized professional who does exactly that kind of work. [br]
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https://www.reddit.com/r/Quest2/comments/119pjnn/re_can_you_upgrade_the_quest_2_storage_yes_it_is/