Here's what I've found so far. In case it helps someone.

1. My iPhone was on Low Battery Mode
2. I connected it to my mac, opened XCode > Window > Devices & Simulators
3. Select Allow on my mac
4. Select Trust on my iPhone
5. Now Developer Mode is showing in Privacy & Security

Here’s what I have found:

1. My iPhone was on “Low Battery Mode.”
2. I connected it to my Mac and opened “XCode > Window > Devices & Simulators.”
3. Select “Allow” on my mac
4. Select “Trust” on my iPhone
5. Now “Developer Mode” is showing in “Privacy & Security.”