I am new here and using an TP link archer c50 v3 EU, I have installed OpenWrt to use the router as nat6 to make our devices "invisible" for our ISP, but it doesn't work at all after following the quid he still can't ping googles IPv6 (the client) if I ping from the router it works. And before this guide IPv6 didn't work at all windows told me if I ping he can't find a host www.google.de or something like that, what can I do to get it to run? And if it will run, is there any way to build the firmware with the needed chances?
Another blind guessing attempt: Are you running a „router behind another router“ setup? if your first router does not hand out an IPv6 prefix, the second router would not have working IPv6.
you are drip-feeding additional information. That isn‘t helpful.
You likely also need to put in more structure into your debugging: You need to fix your IPv6 base problems before compiling custom firmware or configuring NAT6 add-ons: Install the default image, check your IPv6. Once that works, gradually add more config. Once everything works as expected, save your config and start building a custom image.
If you get stuck anywhere on that way, describe the detailed path up till the problem in a structured way.
So you have compiled custom firmware. I doubt that that expertise came from thin air. You likely have read some documentation to do so. Would documentation like „and then compile your custom firmware or something like that“ have helped you to learn that? Now think of someone reading your problem level of detail, having to guess what could have happened.
OpenWrt 21.02 does not support NAT6 out of the box. Since you didn't post any information about custom iptables commands, scripts or additional packages installed I guess you incorrectly assumed that OpenWrt would perform NAT6?
IPv6 masquerade capabilities are not available by default (needs extra iptables packages) nor exposed in the firewall configuration. You would need to implement custom iptables commands translating the ULA range (or any other local addressing scheme you implemented) to your OpenWrt routers WAN-side GUA.