Hi Jeroen1541,
Thanks for reaching out.
It appears to me that the ads between your posts on the start page are AdSense Auto Ads. These are placed and controlled completely by AdSense. There are some limited options to control their appearance in your AdSense account.
If you enabled Auto ads through Advanced Ads then you can remove their code in Advanced Ads > Settings > AdSense > Verification code & Auto ads.
However, AdSense can also inject Auto Ads through individual ad units. You can only disable that behavior directly in your AdSense account. Go to your AdSense Dashboard > Ads > Overview > By site, then click on your website and disable Auto ads in the Ad Settings section.
You can follow this tutorial and learn how to place AdSense ads manually on your site. This makes sure that AdSense ads will appear on positions of your choice on mobile and desktop, as well as between posts.
Please let me know if you need anything else.
Best regards,
Henning