https://launchpad.support.sap.com/#/notes/2305401 (App to App Navigation CookBook.pdf)
https://blogs.sap.com/2020/07/31/fiori-my-inbox-integration-of-custom-detail-page/
Target:
Go to /n/ui2/fpld_cust and define a second target for your App, i.e. approve.

The approve target needs the “emdedIntoDetails” parameter:

SWFVISU:
Add the new target for your WF Task. Here you have access to all attributes of your Workitem-Container. Pass all your mandatory fields you’ve defined in your oData Entity.
Some examples: https://blogs.sap.com/2016/05/31/my-inbox-open-task-swfvisu-configuration/

If your missing some parameters, just add them in your Workitem Task and pass the values directly into it right from your Workflow Container. This looks much better.

Manifest:
Add a route to navigate via Inbox. The pattern has to match your inbox url.

"routes": [ { "pattern": "", "name": "master", "target": "master" }, { "pattern": "DataSet/{Pernr},{Datum},{Infty}", "name": "object", "target": [ "master", "object" ] }, { "pattern": "detail/LOCAL_INBOX/{wfInstanceId}/{taskPath}", "name": "wfobject", "target": "object" }
Detail.Controller:
onInit: function () { // Model used to manipulate control states. The chosen values make sure, // detail page is busy indication immediately so there is no break in // between the busy indication for loading the view's meta data var oViewModel = new JSONModel({ busy: false, delay: 0 }); this.getRouter().getRoute("object").attachPatternMatched(this._onObjectMatched, this); //My Inbox Integration this.getRouter().getRoute("wfobject").attachPatternMatched(this._onWFObjectMatched, this); this.setModel(oViewModel, "detailView"); this.getOwnerComponent().getModel().metadataLoaded().then(this._onMetadataLoaded.bind(this)); }, _onWFObjectMatched: function (oEvent) { this.getModel("appView").setProperty("/layout", "MidColumnFullScreen"); var compData = this.getOwnerComponent().getComponentData(); if (compData && compData.startupParameters && compData.startupParameters.PERNR && Array.isArray(compData.startupParameters.PERNR) && compData.startupParameters.PERNR[0]) { var sPernr = compData.startupParameters.PERNR[0]; var sDatum = compData.startupParameters.DATUM[0]; var sInfty = compData.startupParameters.INFTY[0]; this.byId("detailPage").addStyleClass("myInboxPage"); this.getModel().metadataLoaded().then(function () { var sObjectPath = this.getModel().createKey("/DataSet", { Pernr: sPernr, Datum: sDatum, Infty: sInfty }); this._bindView(sObjectPath); }.bind(this)); } },