Upon trying to install features in Windows server 2019 I received error 0x80073701 _sxs_assembly_missing
Not very obvious why this suddenly happened, but in my case this was due to missing system files in the dism image or probably rather a registry entry suggesting a language for a patch that was not installed.
I searched the c:\Windows\Logs\CBS\CBS.log file for sxs_assembly_missing and found a line that pointed to update KB5007206
I downloaded this patch from https://www.catalog.update.microsoft.com
I then extracted files with the following command
expand -F:* C:\IT\windows10.0-kb5007206-x64_f8ccc7d4574581576e74d86ccacc7fbf47d050f6.mus c:\it\cab
I then injected the patch in the system image with dism and the following command:
dism /online /add-package /packagepath:c:\it\cab\Windows10.0-KB5007206-x64.cab
Then the feature installs were back and working again.
I spent a couple of hours on this mess.. hope this helps someone 🙂