To insert a comma or other separator between Tags or Categories in the Template (%post_tag% or %category%) use the :after CSS pseudo class and add this selector to your Customizer.
CSS to add a comma between https://print-plus.ca/ajx6d7epegx Tags:
. https://samede.org/2023/03/14/bpggnmi8 cat-post-tax-post_tag a:not(:last-child):after
{
content:",";
}
CSS to add a comma between Categories:
. cat-post-tax-category a:not(:last-child):after
{
content:",";
}