Comment by immibis
These are all defaults, by the way. Subnets don't have to be /64 - that ended up being the default by historical accident; though it's nice that it forces every ISP to give you at least a /64 which you can subnet further if you want to, though without SLAAC.
Privacy addresses should be used for outgoing connections. Don't treat one as a static address. If you need to write down an address, give that machine an easily remembered static one.
I feel like residential ipv6 would be at least a little further along if routers simply always enabled NAT by default for it, like what cell providers do. Solves all these questions and problems for inexperienced users. Instead, you gotta ask, is the firewall enabled and default-deny, are ULAs enabled...