@Devon van de Kletersteeg , I believe in the new UI it has been removed. I'm making an assumption here that you are on version 8.x. If so you should have 2 options.
1. Add the epic link to the new issues when creating.
2. Drag the issues to the epic in the backlog view.
Take a look at this Atlassian document for some additional information:
We’re excited to introduce external collaboration for Confluence, now available in early access. It is available to preview for Confluence Cloud Premium and Enterprise customers. (If you're not on ...
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