Lukas4104,
I see your issue, you should be getting a tabular format when you add the connector...

The connector will let you switch between Text Mode and Key Value mode and it looks like you're in Text Mode. There should be a small icon that you can click to switch but I don't see it present in your image.
You can still use Text Mode to get this to work, like the below example...
Accept: application/json; odata=nometadata
For more:
https://docs.microsoft.com/en-us/sharepoint/dev/business-apps/power-automate/guidance/working-with-send-sp-http-request
If this is a connector from an older Flow, that may be the issue. You should just have to recreate the connector in that case.
If this is a connector from a new Flow, then this may be something else...
- Could be a resolution issue, we dynamically size this content and things will be taken out if the resolution doesn't support it. The button I'm referring to could be getting cut out.
- It may be expected for the connector for some other reason, possibly due to the formatting of a non-English language. This would be similar to the above point, it may just be getting cut out.
Let us know!
Sincerely,
Patrick