A few things:
- Ctrl+Alt+0 makes the Scene’s active camera jump to your current viewport view.
- The render region has sliders but they’re not in an obvious place. You’ll find them in the Outliner, Data API mode, Scenes > Your Scene > Render Data > Region Minimum X/Y, Maximum X/Y:
These sliders are a multiple of the Render output resolution (from 0 to 1)
- If you want to literally convert your region into the camera itself (with the corresponding output resolution), you can use my addon: Camera Regions. Ask over in this other thread if you have questions.
