Even though anchor links don't work in all mail clients, we have still been using them in emails for tables of content in a monthly newsletter. It seems like at least a few others have run into the same problem we have, which is that Mosaico breaks anchor links:
How can I set up anchors in Mosaico mailing? Internal links in a Mosaico template?
I've found that the issue is actually because Flexmailer seems to try to apply tracking to all URLs, including anchor links, which breaks them. I've put those details here:
https://github.com/civicrm/org.civicrm.flexmailer/issues/43
Does anyone have ideas how this could be fixed simply?