Hi DIE PIC,
I do not think you can do it with Power Automate as the List rows action of dataverse is not showing the PrincipalObjectAccess.

I have done it with the help of JS. Here is the code:
// A namespace defined for the sample code
// As a best practice, you should always define
// a unique namespace for your libraries
var Test = window.Test || {};
(function () {
// Define some global variables
let entitysPluralName = {
PrincipalObjectAccesss: "principalobjectaccessset"
};
let globalVariables = {
Results: "",
WebAPIVersion: "v9.1"
};
this.retrievePrincipalObjectAccess = function () {
try {
var fetchData = {
opportunityid: this.getId()
};
var fetchXmlQuery = [
"<fetch>",
" <entity name='principalobjectaccess'>",
" <attribute name='principaltypecode' />",
" <attribute name='principalobjectaccessid' />",
" <attribute name='principalid' />",
" <link-entity name='opportunity' from='ecs_expenseid' to='objectid'>",
" <filter type='and'>",
" <condition attribute='opportunityid' operator='eq' value='", fetchData.opportunityid, "'/>",
" </filter>",
" </link-entity>",
" </entity>",
"</fetch>",
].join("");
this.retrieve(globalVariables.WebAPIVersion, entitysPluralName.PrincipalObjectAccesss, fetchXmlQuery);
if (globalVariables.Results.length > 0) {
//your logic
}
}
catch (e) {
this.openAlertDialog("Error from getId: " + "e: " + e + ". e.mesage: " + e.message);
}
}
this.retrieve = function (webAPIVersion, entitysPluralName, fetchXmlQuery) {
try {
var req = new XMLHttpRequest();
req.open(
"GET",
parent.Xrm.Page.context.getClientUrl() +
"/api/data/" + webAPIVersion + "/" + entitysPluralName + "?fetchXml=" +
encodeURIComponent(fetchXmlQuery),
false
);//Sync
req.setRequestHeader("Prefer", 'odata.include-annotations="*"');
req.onreadystatechange = function () {
if (this.readyState === 4) {
req.onreadystatechange = null;
if (this.status === 200) {
var results = JSON.parse(this.response);
globalVariables.Results = results.value;
} else {
alert(this.statusText);
}
}
};
req.send();
} catch (e) {
this.openAlertDialog("Error from retrieve: " + "e: " + e + ". e.mesage: " + e.message);
}
}
this.getId = function (formContext) {
let iD = "";
try {
iD = formContext.data.entity.getId();
} catch (e) {
this.openAlertDialog("Error from getId: " + "e: " + e + ". e.mesage: " + e.message);
}
return iD;
}
this.openAlertDialog = function (alertStrings) {
try {
Xrm.Navigation.openAlertDialog(alertStrings).then();
} catch (e) {
Xrm.Navigation.openAlertDialog("Error from openAlertDialog: " + "e: " + e + ". e.mesage: " + e.message).then();
}
}
}).call(Test);