All routers I've ever encountered have a default deny rule for IPv6, replicating the port forwarding setup people have come to expect from NAT. Except you can use multiple Xboxes in the same network now, of course.
Even the mini router I bought for 15 bucks five years ago does IPv6 addressing just fine. Just announcing a prefix (or two, local network stuff over ULAs and all that) is enough to make SLAAC do its thing. Never had any problem with DHCPv6 PD for automatic subnetting either.
I haven't looked into UPnP on IPv6 much, but the ones that did UPnP all seem to do IPv6 fine after 2015 or so. I usually turn it off because I don't want random crap manage my firewall unauthenticated (and many router manufacturers have had vulnerable implementations that would accept UPnP packets from the internet so screw that).
Brands that I've successfully used IPv6 with without any hassle include TP-Link, D-Link (don't buy from them), AVM, Mikrotik, and Netgear.
The most annoying part I find about routers is actually that they don't let you disable ALGs anymore it seems. Every few years Samy Kamkar writes up a way to bypass most IPv4 firewalls by abusing the hackery we've accumulated around NAT and the easiest fix ("let FTP/SIP/H363/PPTP be broken on IPv4") doesn't seem to come with routers anymore.
It took a while, but router manufacturers seem to have realised that the world is moving towards "CGNAT or IPv6" and not having usable IPv6 breaks networks in those cases.
The most broken IPv6 deployments I've seen were from people who tried to turn it off though weird hacks like firewall rules which subsequently got IPv6 from their ISP. Had they actually disabled IPv6 they would've just been stuck OK IPv4 like regular, but their weird hacks made half the TCP connections need to time out before they could access the internet.
Even the mini router I bought for 15 bucks five years ago does IPv6 addressing just fine. Just announcing a prefix (or two, local network stuff over ULAs and all that) is enough to make SLAAC do its thing. Never had any problem with DHCPv6 PD for automatic subnetting either.
I haven't looked into UPnP on IPv6 much, but the ones that did UPnP all seem to do IPv6 fine after 2015 or so. I usually turn it off because I don't want random crap manage my firewall unauthenticated (and many router manufacturers have had vulnerable implementations that would accept UPnP packets from the internet so screw that).
Brands that I've successfully used IPv6 with without any hassle include TP-Link, D-Link (don't buy from them), AVM, Mikrotik, and Netgear.
The most annoying part I find about routers is actually that they don't let you disable ALGs anymore it seems. Every few years Samy Kamkar writes up a way to bypass most IPv4 firewalls by abusing the hackery we've accumulated around NAT and the easiest fix ("let FTP/SIP/H363/PPTP be broken on IPv4") doesn't seem to come with routers anymore.
It took a while, but router manufacturers seem to have realised that the world is moving towards "CGNAT or IPv6" and not having usable IPv6 breaks networks in those cases.
The most broken IPv6 deployments I've seen were from people who tried to turn it off though weird hacks like firewall rules which subsequently got IPv6 from their ISP. Had they actually disabled IPv6 they would've just been stuck OK IPv4 like regular, but their weird hacks made half the TCP connections need to time out before they could access the internet.