Hello Jamie Williams
Firstly, apologies for the delay in responding here and any inconvenience this issue may have caused.
I checked with internal team on this, WAC .MSI installer temp file was blocked by the Windows Defender Application Control (WDAC), which caused the WAC installation failure. Team is working on getting this fixed.
Changing the policy to Audit mode will resolve this issue. So you can use this as a temporary workaround till the fix is rolled out.
Hope this helps.
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