Sorry to hear that, about your experience with the recent updates on your Samsung Galaxy A12 Nacho having issues with internet connectivity as well as with notification and display brightness and we apologize for the inconvenience it caused you.
Submit an error report through Samsung Members app as follows:
Step 1. Long press Samsung Members icon on Apps screen and tap Error reports.
Step 2. Tap OK on agreement popup to send system log data.
Step 3. Select Symptom category "Networking/Wi-Fi" and "Settings/System".
Step 4. Describe the problem in details and SEND.
How to submit an error report on Samsung Members app? | Samsung PH
Also, you can check by calling the Customer support of your Mobile Network Services provider in order to find out the status of signal in your coverage area.
If the problem persists, immediately bring your device to the nearest Samsung Authorized Service Center. Rest assured that our Samsung Engineers/Technicians are competent to assess your device and offer solutions to restore it up to optimum performance.
For more assistance, you may contact us on our online Samsung support channels below.