[kimberly]

You
8:31 pm
Hello, I haven't been using my tecno G9 for about 2+ years now since my phone has been acting up. It has pop ups stating that something harmful has been installed. Some random app stopped working and so on. There seems to be nothing wrong with the hardware. I just don't know how to resolve this issue.

I had flashed my phone using one of the links provided here. Now the IMEI number is also not visible

[X3non]

You
8:31 pm
Hello, I haven't been using my tecno G9 for about 2+ years now since my phone has been acting up. It has pop ups stating that something harmful has been installed. Some random app stopped working and so on. There seems to be nothing wrong with the hardware. I just don't know how to resolve this issue.

I had flashed my phone using one of the links provided here. Now the IMEI number is also not visible

ensure that the baseband isn't unknown, see https://www.hovatek.com/forum/thread-21069.html
you can fix imei using engineering mode @ https://www.hovatek.com/forum/thread-116.html

[hovatek]

...
I had flashed my phone using one of the links provided here. Now the IMEI number is also not visible

Did flashing fix the popups and errors (before we focus on IMEI issue)?