Hi @OrcaDeWils
Thank you for posting.
According to your description, you would like to update item properties when file is created. But due to SPO internal feature ‘checkin/checkout’ enabled, the trigger is not able to detect the new file creation directly.
Actually, it’s normal behavior as flow can’t detect file checkout/checkin shatus by design. There aren't any triggers available for this. But we do have workaround for this to use ‘send an http request to sharepoint’ instead.
Steps are:
"when file is created or modified"
"Send a HTTP Request to SharePoint"
Parse JSON
Check Condition
is status == checked in, then do something, else terminate
HTTP URI is :
_api/web/getFileByServerRelativeUrl('/sites/TestFileShare/@{body('Get_file_properties')['{Path}']}@{body('Get_file_properties')['{FilenameWithExtension}']}')/checkOutType



https://powerusers.microsoft.com/t5/Building-Flows/Invoke-a-trigger-on-check-in-of-document/td-p/96062
If you would like this feature to be added in Microsoft Flow, please go to this link and vote here:
https://powerusers.microsoft.com/t5/Power-Automate-Ideas/SharePoint-trigger-for-File-Checked-Out/idi-p/553062
Hope the content above may help you.
Thanks
Anna