Is the GL.iNet GL-MT300N-V2 the glue between T-Mobil Home internet and multiplayer Xbox Series X?

Install 464XLAT, 464xlat will provide clat service on the router, automatically start nat46, and find the superior plat service, but the automatic effect is not very good, you can manually add the configuration.
You can add under the /etc/config/network file, configure as follows,

config interface ‘wan6_4’
option proto ‘464xlat’
option ip6prefix ‘dd50:e735:b42d:1111::/96’

and then execute cmd: /etc/init.d/network restart
Option ip6prefix is just an example. This is the ipv6 prefix of a NAT64 server. It is usually provided by the operator. You can ask the operator.