G: Here’s how to make the screen brighter on your iPhone 12:

Quick steps:

Open Settings > Display & Brightness.
Drag the Brightness slider to the right.

Faster method:

Swipe down from the top-right corner of the screen to open Control Center.
Drag the Brightness bar (it looks like a sun) upward.

Would you also want tips to make it even brighter outdoors (like disabling auto-brightness or True Tone)?

G: Got it — sounds like Auto-Brightness or True Tone is fighting you. Here's how to fix it:

1. Turn off Auto-Brightness
(This stops the phone from dimming on its own based on light.)

Open Settings > Accessibility > Display & Text Size.
Scroll down and turn off Auto-Brightness.

2. Turn off True Tone
(True Tone adjusts colors and brightness to match your environment, sometimes making the screen look dimmer.)

Open Settings > Display & Brightness.
Turn off True Tone.

3. (Optional) Turn off Night Shift
(Night Shift can also make the screen look dimmer/yellower at certain times.)

Same place: Settings > Display & Brightness > Night Shift.
Make sure it’s off.

Quick TLDR:
Auto-Brightness off = full manual control.
True Tone off = screen stays as bright as you set it.
Night Shift off = no automatic color dimming at night.

If you want, I can also show you how to add a permanent manual brightness shortcut to your Control Center. Would you like that?

G: Understood — if Auto-Brightness, True Tone, and Night Shift are already off, and it’s still too dim even on cloudy days, then it’s likely one of these issues:

Possible causes:

Low Power Mode is on
(It reduces maximum brightness to save battery.)

Check in Settings > Battery. If Low Power Mode is on, turn it off.
Brightness limit glitch
(Sometimes iOS gets stuck at a lower brightness ceiling until you reboot.)

Try fully powering off your phone (not just locking it) and turning it back on.
Hardware issue
(If the screen or backlight is failing, brightness won’t go higher no matter what.)

Usually shows as "dim even at 100%" and often gets worse over weeks/months.
Display Zoom
(Rare, but if enabled, sometimes brightness behaves weird.)

Check Settings > Display & Brightness > Display Zoom > View and make sure it’s on Standard.

Quick checklist to fix:

Low Power Mode OFF
Phone rebooted
Display Zoom set to Standard
Screen not visibly damaged

If it's still dim after that, there's a good chance the backlight is weakening (common after 2–4 years depending on usage).
If you want, I can tell you quick ways to check if it’s a hardware problem without going to Apple yet.

G: That definitely means something is still auto-adjusting it behind your back.

Here’s what could still be active:

1. Attention-Aware Features
(If your iPhone thinks you're not looking at it, it dims automatically.)

Go to Settings > Face ID & Passcode.
Find Attention-Aware Features and turn it off.

This is almost always the culprit when brightness changes even after everything else is off.

2. True Hardware Problem (Less Likely)
If it flickers or brightness pulses without touching the phone at all, it could be a sensor or screen hardware issue (like a faulty ambient light sensor, even if Auto-Brightness is "off").

Bottom line for your case right now:
Turn off Attention-Aware Features and that should kill all remaining automatic brightness changes.

Let me know if it’s still happening after that, and we’ll dig deeper if needed.

G: Yes. That absolutely narrows it down — this sounds like a thermal throttling or GPU fault, not a software brightness setting.

Here’s what the symptoms point to:

1. Thermal Dimming / Throttling

iPhones automatically dim the screen when they overheat, even if Auto-Brightness is off.
Launching the Camera uses the GPU + image processing, which heats up the phone fast, especially if it's already warm or charging.

You’d see:

Sudden dimming you cannot override
Jittery UI
Lag or ghosting when trying to swipe or use Control Center
Phone may feel warmer than usual on the back near the camera

Fix:
Let the phone cool down. Turn it off for 5–10 minutes if needed. Don’t use camera or bright screen while charging if it’s hot.

2. Power Delivery Glitch / Battery Issue
If the battery is failing or iOS is mismanaging power delivery, the screen dims to prevent shutdown.

Check this:

Go to Settings > Battery > Battery Health & Charging
- Look at Maximum Capacity (if it’s under 80%, that’s a red flag)
- Look for any “Service” warning at the top

What you’re describing isn’t normal — it’s hardware-driven auto-protection, most likely thermal or electrical. Not your fault.
Once triggered, it disables your ability to change brightness until it resets.

If you want to test it:

Use the phone with brightness at max for a while
Open the camera or record video
Feel the phone: does it get warm? Does the dimming kick in the same way?

If yes: it’s likely overheating or battery failing under load.
Let me know your battery capacity %, and I can tell you if this is something Apple might repair (or if there’s a DIY approach).