Using the Internet without IPv4 connectivity

I'm in the same situation myself. It's quite frustrating, since 2 weeks I have been told that "the ticket is open and the technicians will take a look soon". Not sure if stuff like this has a low priority since IPv6 works and it's not considered a total outtage? In Germany there are laws to grant consumers compensation in those cases, but I'll see if this counts soon enough.

One problem with the solution in this blog post is that various endpoints block datacenter IP ranges entirely or make you go through various captcha hoops, but no good way around that. Same for common VPN providers.

Since I wanted to fix this for my entire home network I also had to do this on my router - in those cases it's quite beneficial to have a non-standard device like an Ubiquiti EdgeRouter, not sure how I would have set up all the Wireguard routing and nat rules on something like a FritzBox. The only downside is that the Router isn't powerful enough to handle a lot of connections, so I'll have to switch to IPSec which is supported by hardware offloading.

Fritzbox actually has some very nice GUI steps for configuring a VPN connection, intended for Fritzbox to Fritzbox connections but any compatible VPN will do. It also allows setting up static IPv4/IPv6 routes (Home Network>Network>Network Settings>Additional settings>IPv4 routes/IPv6 routes).

The biggest problem you'd probably run into is figuring out what kind of IPsec encryption configuration the router expects from the other side (Wireguard should be a lot easier but then you may run into hardware acceleration issues).

If you need to get down to it, you can also make a backup of the Fritzbox config file, edit the dump to manually configure the VPN endpoint, recalculate the checksum (there are tools for that), and re-import the config file. AVM has loads of config not accessible to the user that you can tweak that way, but they make it a bit hard to access so you don't accidentally brick your router.