For number of reasons, instead of migration, I should write migraine. First is about moving from an old system into a new one. Latter is about medical condition causing severe headaches. In this case, there seems to be not much of a difference.
Google's own Make the switch to Google Analytics 4 -migration guide has 12 steps. Given complexity, the time I have to invest on this and lack of really diving into this, I probably missed most of them.
Going into GA4-console, I have this:
Clicking on Get Tagging Instructions, I'll get further information:
<script async="" src="https://www.googletagmanager.com/gtag/js?id=G-859QZJED94"></script>
window.dataLayer = window.dataLayer || ;
gtag('js', new Date());
Note: My GA4-stream ID is G-859QZJED94. Make sure to use yours, not mine. As the stream ID cannot be a secret, it's ok to publish it here. The same ID can be found from HTML-code of this page.
To verify installation success, I went to GA4 portal, chose Reports and Realtime. It didn't take long, less than a minute, for that report to indicate user activity. Many other places keep saying "No data received from your website yet", "No data received in past 48 hours" or "Data collection isn’t active for your website". IMHO all of those are incorrect, as I do have stats. We'll see if I managed to do that right.