Seems like content policies have changed and now links are allowed under the condition that they are explicit enough:
4.6 Off-site linking:
4.6.1 Off-site links may not refer users to sites that deliver functionality effectively similar to that available on Twitch.tv.
4.6.2 Off-site linking elements must have a visible indicator to signify that it will take the user off-site, such as link text, or a button.
There is nothing about what type of extension you’re using (overlay or not).
Still, I’m not able to make a link work in my overlay extension unless I right-click it and open it in a new tab… 