IPv6 not working with NAT6 and before

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?

I hope anyone can help me

OpenWRT="OpenWrt 21.02.3 r16554-1d4dea6d4f"

did you migrate this device from OpenWRT v19 to v21, while preserving all old config settings?

No the device is flashed with this version from an default firmware

And I have restored(factory settings) it multiple times

Maybe important: actually we have an dynamic IPv6 prefix from our provider but I want to ask the new (chance 18.8.2022) if we can get an static (for docker and servers etc)

Firmware is self compiled I post the build command at the day

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.

We have a fritzbox as DSL router, the OpenWrt router is behind the fritzbox. The OpenWrt router has an IPv6 from the Fritzbox, ifconfig on the OpenWrt give me this output:

br-lan    Link encap:Ethernet  HWaddr 50:C7:BF:D0:6B:B9
          inet addr:192.168.1.1  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fd54:8784:b55::1/60 Scope:Global
          inet6 addr: fe80::52c7:bfff:fed0:6bb9/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2833 errors:0 dropped:0 overruns:0 frame:0
          TX packets:2294 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:470923 (459.8 KiB)  TX bytes:980253 (957.2 KiB)

eth0      Link encap:Ethernet  HWaddr 50:C7:BF:D0:6B:B9
          inet6 addr: fe80::52c7:bfff:fed0:6bb9/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:5997 errors:0 dropped:6 overruns:0 frame:0
          TX packets:4821 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:1372384 (1.3 MiB)  TX bytes:1420389 (1.3 MiB)
          Interrupt:5

eth0.1    Link encap:Ethernet  HWaddr 50:C7:BF:D0:6B:B9
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2837 errors:0 dropped:4 overruns:0 frame:0
          TX packets:2386 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:471107 (460.0 KiB)  TX bytes:985221 (962.1 KiB)

eth0.2    Link encap:Ethernet  HWaddr 50:C7:BF:D0:6B:BA
          inet addr:192.168.178.110  Bcast:192.168.178.255  Mask:255.255.255.0
          inet6 addr: fd54:8784:b55:12::1/64 Scope:Global
          inet6 addr: fe80::52c7:bfff:fed0:6bba/64 Scope:Link
          inet6 addr: 2003:c2:bf34:c400:52c7:bfff:fed0:6bba/64 Scope:Global
          inet6 addr: fd54:8784:b55:11::1/64 Scope:Global
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:3098 errors:0 dropped:331 overruns:0 frame:0
          TX packets:2414 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:790627 (772.0 KiB)  TX bytes:411992 (402.3 KiB)

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:591 errors:0 dropped:0 overruns:0 frame:0
          TX packets:591 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:60359 (58.9 KiB)  TX bytes:60359 (58.9 KiB)

and the custom image has only additional software no chanced configurations

the command was

make image  PROFILE=tplink_archer-c50-v3 PACKAGES='luci luci-ssl luci-i18n-base-en luci-i18n-base-de tinyproxy luci-app-tinyproxy luci-i18n-tinyproxy-de luci-i18n-tinyproxy-en nano-full luci-app-ddns luci-app-https-dns-proxy luci-i18n-https-dns-proxy-de luci-i18n-https-dns-proxy-en luci-i18n-ddns-de luci-i18n-ddns-en'

i will try now the default software

Now i have flashed it with (https://downloads.openwrt.org/releases/21.02.3/targets/ramips/mt76x8/openwrt-21.02.3-ramips-mt76x8-tplink_archer-c50-v3-squashfs-sysupgrade.bin) without saving configurations but on my pc I still can't ping google via IPv6

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.