hi @g29h9ZjS4Y2d42FmCG9D, if you are running your own instance you can edit the templates directly. Look in the directory templates/, you will probably want to add it to the <head> of the file base.tmpl.
I would suggest creating a new file like matomo.tmpl, which will contain the script to be included. It will look something like this:
{{ define "matomo" }}
<!-- matomo script -->
<script type="text/javascript">
// all the script contents here
</script>
<!-- end matomo script -->
{{ end }}
then you can include this template in any of the other templates with {{ template "matomo" }}.