$compute Arithmetic Operators with DateTime, Duration not working as expected

Assemblies affected: ASP.NET Core OData 8.0.8

Due to lack of documentation, OData is an obscure framework to use.
According to this OData v4 documentation http://docs.oasis-open.org/odata/odata/v4.01/odata-v4.01-part2-url-conventions.html#sec_ArithmeticOperators, when we use $compute=InitialDate sub now() the returned value should be an Edm.Duration being InitialDate and now() Edm.DateTimeOffset. when we call $compute=InitialDate sub duration'P2D' the returned value should be an Edm.DateTimeOffset.

Both calls return cast excepetion, unless we cast the result to Edm.String. The problem is we can't parse that string to use in a $filter or something like that.

Reproduce steps
Run: $compute=now() sub 2021-01-01T00:00:00-00:00 as TimeToYearStart
Or: $compute=now() sub duration'P7D' as LastWeek

Expected behavior
TimeToCentury: ~ duration'P100D'
LastWeek: ~ 2021-04-01T00:00:00-00:00

Workaround
$compute=cast(now() sub 2021-01-01T00:00:00-00:00, Edm.String) as TimeToYearStart
$compute=cast(now() sub duration'P7D', Edm.String) as LastWeek

TimeToYearStart: "220305172941.000000"
LastWeek: "20220404493051.000000"

Screenshots

Additional context
If someone has any updated documentation, please share! We shouldn't have to read all the source code of a framework in order to use it