ok, i don't have a multishop, but for a "single" shop setup this works for me:
You create your GA4 tag in google analytics first.
You will get code like this, change the id G-58HPYXXXXX to your own id.
<!-- Global site tag (gtag.js) - Google Analytics -->
<script async src="https://www.googletagmanager.com/gtag/js?id=G-58HPYXXXXX"></script>
<script>
window.dataLayer = window.dataLayer || [];
function gtag(){dataLayer.push(arguments);}
gtag('js', new Date());
gtag('config', 'G-58HPYXXXXX');
</script>
copy this code in: (instellingen is dutch for Settings)