Where in Settings can I allow apps from a developer (myself)

I eventually gave up and payed for a subscription and obviously it worked. But I was told by Apple support that a paying subscription is not mandatory for this to work. But they didn’t help me further because I didn’t have a paying subscription. 😅 oh well…

After a lot of research, I figure it out. Goto Setting > VPN & Device management and at the bottom section of "Developer App" there must be your name listed as Apple Development: "Your name", Click on it then click Trust "Apple Development: Your Name"; A prompt will open asking Trust, Hit Trust. Then go to the app and it will surely work fine on your phone.

I had the same issue today, successfully resolved with a free developer account and iOS 15.2.

The error popup wasn't helpful in that it didn't say where under Settings to allow the developer. Looking for which category to find this option under, I saw the (correct) answer by msjg and this worked for me. The one point I'd like to add as no one seems to have mentioned this yet is that in order for your developer account to show up under VPN and Device Management, Xcode has to actually be attempting to run the app on your phone at the time. The first time I tried the same thing without connecting the device to the computer and without having Xcode running, I ran into the same issue as other users not seeing any profiles to trust.

So, -- Follow the steps in the answer by msjg AND -- Do this while your phone is connected and Xcode is open and attempting to run the app.

Keep in mind that an internet connection is required