Do local nodes work across crypto types? Newbie to all of this, hoping you can help with what is probably a "duh" question. I'll keep it brief, though: if I download the blockchain using the instructions given for the Bitcoin GUI, will I be able to use it as a local node for my Monero GUI wallet, as well?

Thanks so much! :)
No, while there are some wallets that support multiple coins, the full nodes of each cryptocurrency network generally have their own distinct node software. In particular Monero and Bitcoin will require separate software.