As this is probably the most seen post online, here is the solution.
Load your custom CA CERT / SSL Cert (burp suite or whatever)
Enable Developer Mode
Using ADB, type ./adb shell monkey -p com.android.settings -v 500
This command will open the Settings modal. You might see the list of all your apps, or the complete settings menu..
Just click on the arrow on the top left to come back to the main menu if you see the list of all apps.
From there, scroll down to "Security -> Encryption & Credentials -> Install Certificate"
As this is probably the most seen post online, here is the solution.
Load your custom CA CERT / SSL Cert (burp suite or whatever)
From there, scroll down to "Security -> Encryption & Credentials -> Install Certificate"
Enjoy