Thanks, but it does not have to be 8080. I use 80 in my KeyCloak dev instance for example. The registered targets need to use the container port (which is 8080), but the target groups port can be 80. But I do think I forgot to open port 8080 in the security group like Adi mentioned.

This is my target group:
https://imgur.com/a/KNGuEDz

And my registered targets:
https://imgur.com/a/ddffvg5