Pinia store detection question

[pietk4]

When I setting up pinia with Vue3 application in the following way:

import { createApp } from "vue";
import { createPinia } from 'pinia';
import Page from "./components/Page.vue";

const app = createApp(Page);
const pinia = createPinia();
app.use(pinia);
app.mount("#app");

My stores are properly detected by Vue devtools, as shown in following screen:

But when I move pinia part to separate plugin file:

// piniaPlugin.js
import { createPinia } from 'pinia';
const pinia = createPinia();
export default pinia;

//app.js
import { createApp } from "vue";
import piniaPlugin from './piniaPlugin';
import Page from "./components/Page.vue";

const app = createApp(Page);
app.use(piniaPlugin);
app.mount("#app");

My stores are not detected as "installed" (I don't see those lines in console) and there are no changes recorded for them in "Timeline" section.
(Pinia plugin itself is detected properly by Vue devtools and I can see my stores content there, only Timeline part is not working)

What I'm doing wrong?