Since I noticed my button icons are normal sized in other views I guessed that it's because of the sap.m.MessagePage element.
Is there a nice solution for this or did the developers just wanted us to never use icons inside of buttons in that element? :D
globalThis.onUI5Init = () => sap.ui.require([
"sap/ui/core/mvc/XMLView"
], async XMLView => (await XMLView.create({
definition: document.getElementById("myxmlview").textContent,
height: "100%",
})).placeAt("content"));<script defer id="sap-ui-bootstrap"
src="https://openui5.hana.ondemand.com/resources/sap-ui-core.js"
data-sap-ui-oninit="onUI5Init"
data-sap-ui-libs="sap.ui.core,sap.m"
data-sap-ui-theme="sap_fiori_3"
data-sap-ui-async="true"
data-sap-ui-compatversion="edge"
data-sap-ui-excludejquerycompat="true"
data-sap-ui-xx-waitfortheme="init"
></script>
<!-- Issue fully reproducible with UI5 <= 1.87 and partially reproducible until 1.93 -->
<script id="myxmlview" type="text/xml">
<mvc:View xmlns:mvc="sap.ui.core.mvc" xmlns="sap.m" displayBlock="true">
<App>
<MessagePage showHeader="false" icon="sap-icon://sap-ui5" text="UI5" description="sap.m.MessagePage">
<buttons>
<Button icon="sap-icon://message-warning" text="Change security settings" />
</buttons>
</MessagePage>
</App>
</mvc:View>
</script>
<body id="content" class="sapUiBody">
</body>