Can we start using R5 version

I am submitting ImagingStudy Resource of version 5 but it is still giving below error

"issue": [
{
"severity": "error",
"code": "invalid",
"diagnostics": "Error occurred when parsing model: 'Type checking the data: Encountered unknown element 'partOf' at location 'Resource.partOf[0]' while parsing'."
}
]

I am running R5.Web project but I think it is still using R4 firely version. Is there any change required so that I can use R5 resource

[AB#104742](https://microsofthealth.visualstudio.com/f8da5110-49b1-4e9f-9022-2f58b6124ff9/_workitems/edit/104742)

Start in the R5.Web project by checking which FHIR version is configured for resource parsing, then reproduce the ImagingStudy R5 request that reports the unknown Resource.partOf element. Confirm whether R5.Web is using R4 behavior and identify the project change needed for the request to parse successfully.

Written by the indexing model from the issue text.