Hello 12Hormonen,
Based on your post it appears you’re experiencing issues connecting to Wi-Fi on your iPhone 11. You've done a great job troubleshooting so far. We'll be happy to assist.
Have there been any recent changes to the device or network before experiencing this?
Have you been able to test using different Wi-Fi networks?
Are there any other devices on the network exhibiting the same behavior?
Also, have you tried testing the connection after temporarily disabling LTE?
Once you test that you can also see if the issue continues toggling Bluetooth off temporarily.
We would also recommend restarting the network if possible, then resetting the network settings on the iPhone. Keep in mind, this also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you’ve used before.
Take a look at the articles below and keep us updated.
If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network
Recommended settings for Wi-Fi routers and access points
Cheers!