Hi Guys,
I have a GL-AX1800 running with stock firmware 4.2.3 release1 from their website.
OpenWrt 21.02-SNAPSHOT r16399+159-c67509efd7 / LuCI openwrt-22.03 branch git-21.284.67084-e4d24f0
I've got the following packages installed:

MiniUPnP ACLs set up as default for now.
Xbox still has moderate NAT.
Any help appreciated.
It appears you are using firmware that is not from the official OpenWrt project.
When using forks/offshoots/vendor-specific builds that are "based on OpenWrt", there may be many differences compared to the official versions (hosted by OpenWrt.org). Some of these customizations may fundamentally change the way that OpenWrt works. You might need help from people with specific/specialized knowledge about the firmware you are using, so it is possible that advice you get here may not be useful.
You may find that the best options are:
- Install an official version of OpenWrt, if your device is supported (see https://firmware-selector.openwrt.org).
- Ask for help from the maintainer(s) or user community of the specific firmware that you are using.
- Provide the source code for the firmware so that users on this forum can understand how your firmware works (OpenWrt forum users are volunteers, so somebody might look at the code if they have time and are interested in your issue).
If you believe that this specific issue is common to generic/official OpenWrt and/or the maintainers of your build have indicated as such, please feel free to clarify.