Hi Stefhan,
Thanks so much for reaching out!
Just to let you know, we are limited by our Support Policy in how much we can help with customizations, but I will try to point you in the right direction.
Our Themer’s Guide is a great place to start. You can use the tooltip from the Month View as your guide, and then copy and edit the mini calendar widget template into your theme files.
If this functionality is a requirement for your intended project, I’d suggest that a third-party developer would be the best way to make this feature happen on a short timeline. ? We maintain a list of developers who work with our plugins on our Knowledgebase here:
https://theeventscalendar.com/knowledgebase/find-a-customizer/
Let me know how it goes!
Thanks,
Jaime