I wanted to use an older Raspbian 9 (Stretch) version of 2017/2018 because I wanted to use the "perf" tool which is not available for the current version.
But the previous version was not able to boot by Raspberry Pi 3A+ (no green / ACT light on Raspberry Pi 3A+).
Hence I inserted that SD card in Raspberry Pi Zero and ran commands:
sudo apt-get update sudo apt-get install --reinstall raspberrypi-bootloader raspberrypi-kernel
Then after that I removed that SD card and inserted in my Raspberry Pi 3A+. The green light was attained successfully, but then my Raspberry Pi 3A+ was not able to connect to my Wi-Fi router.
I again copied/inserted ssh (without any extension) and wpa_supplicant.conf file in the SD card; and re-inserted it into the Raspberry Pi 3A+, but still I couldn't make it connect to my Wi-Fi router.
What could be possibly wrong in my procedure?