Hello Reflecting Mirror,
Based on the information provided in your opening post, and research in our labs, we have determined that what you are seeing is caused by a kernel mismatch between WinRE and the host Windows 10 kernel.
Microsoft release version numbers are somewhat random, and it is not known which build will match which versions (1903, 1909, 2004 etc) until the releases are made public. It's also impossible to read the version from the WIM meta data, though the build is available, so we have to guess the version number to display in RMBuilder. In this case the guess was wrong as we had no knowledge of the final build/release mapping for 202H when RMBuilder was built.
When Windows OS is updated through the built-in 'Windows Updates' tool, rather than the 'Upgrade Assistant', the WinRE .wim file is always updated and the WinRE kernel build will always match the host Windows 10 build. This means the release number can be read from the only place where it's available, the running OS.
The 202H update through the Update Assistant tool did not update the WinRE .wim file and has caused a kernel mismatch. Prior to 202H, the WinRE file and OS kernel versions were the same.
Additionally, when booted into the rescue media the version can be read from the running WinRE OS so will always be correct.
The next update of Reflect will include the build/release mapping for 202H (2004) to enable RMBuilder to display the correct WinRE version in the case of a kernel mismatch.
Gosha - Macrium Support