Wi-Fi and Bluetooth not working properly on my broken iPhone 12

Sounds like your iPhone is severely damaged, especially the chip that holds Wi-Fi and Bluetooth, which can cause it to toggle and gray out. I would suggest service at your nearest Apple Store’s Genius Bar or Apple Authorized Service Provider for your repair options.

Genius Bar Reservation and Apple Support Options - Apple

Sometimes, a simple restart can resolve temporary software glitches. Turn off your iPhone, wait for a few seconds, and then turn it back on.

1. Restart the device. That's it.
2. Still not solved --> Force restart iPhone - Apple Support

Settings > General > Transfer or Reset iPhone > Reset > Reset Network Settings: Only network settings are removed.

• When you reset network settings, previously used networks and VPN settings that weren’t installed by a configuration profile or mobile device management (MDM) are removed. Wi-Fi is turned off and then back on, disconnecting you from any network you’re on. The Wi-Fi and Ask to Join Networks settings remain turned on.
• To remove VPN settings installed by a configuration profile, go to Settings > General > Profiles & Device Management, select the configuration profile, then tap Remove Profile. This also removes other settings and accounts provided by the profile. See Install or remove configuration profiles on iPhone in this guide.
• To remove network settings installed by MDM, go to Settings > General > Profiles & Device Management, select the management, then tap Remove Management. This also removes other settings and certificates provided by MDM. See “Mobile device management (MDM)” in the iOS Deployment Reference.
• Reset your Network Settings. Tap Settings > General > Reset > Reset Network Settings. This also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you've used before.

If the above fails...

Settings > General > Transfer or Reset iPhone > Reset > Reset All Settings: All settings—including network settings, the keyboard dictionary, the Home screen layout, location settings, privacy settings, and Apple Pay cards—are removed or reset to their defaults. No data or media are deleted.

1. Reset All Settings: Return iPhone settings to their defaults - Apple Support:- Return iPhone settings to their defaults
2. You can return settings to their defaults without erasing your content.
3. If you want to save your settings, back up your iPhone before returning them to their defaults. For example, if you’re trying to solve a problem but returning settings to their defaults doesn’t help, you might want to restore your previous settings from a backup.
4. 

Make sure you have the latest updates installed.

1. Update Over-the-Air (OTA) —> Update your iPhone or iPad - Apple Support (IN)
2. Update using iTunes/Finder —> Update your iPhone, iPad, or iPod touch - Apple Support (IN)

If none of the above steps resolve the issue, it is recommended to reach out to Apple Support or visit an authorized service center for further assistance. They can provide specific guidance based on your device model and iOS version.

If nothing above works probably it could be your iPhone may have a WiFi radio or antenna problem. In that case, take your device to an Apple Retail Store or Apple Authorized Service Provider, or contact Apple Support and get the hardware tested and if needed repaired/replaced.

Find Locations - Location Selector - Apple

Contact Apple for support and service - Apple Support 

Get a Genius Bar Reservation and Apple Support Options - Apple

Contact Genius Bar. Manage Reservations - My Reservations - Apple

.iv tried everything

Does "tried everything" include a visit to the Apple Store / Genius Bar or an authorized Apple service shop?

You can find a list of authorized service shops in your area using the link just below:

Find Locations

Your phone is broken. Broken devices don't work well. Expecting anyone on a user to user only forum be able to help you when you admit the phone is very damaged, makes no sense. It's like asking how to drive a car when it is damaged and the steering wheel won't turn. The answer is you either have the car fixed or you buy a new car. And the same applies to your damaged phone. There's no magic wand you wave over a damaged phone. None at all.

Just curious, but did you actually read the Authors post? The phone is severely damaged. They said the following: "the back of my iPhone 12 is broken and bit missing." Your boilerplate response, while possibly good for someone who's phone isn't damaged, really won't help much with a phone truly damaged. Just saying.........