The Samsung Galaxy M42 5G can now be given third party firmware treatment thanks to the availability of the TWRP, a popular custom recovery.
Make sure your bootloader on your Samsung M42 is already unlocked and OEM unlock is enabled, otherwise the installation will fail.
Download and install Samsung Drivers from here.
Download the latest *.tar from here for your Samsung M42,
Download Odin.
If not done before, flash disabled VBMeta with Odin in AP or CP slot.
Turn off your Samsung M42, connect it to PC and reboot to download mode by holding down Volume up, Volume down and power button at the same time.
Open Odin and check if your device is detected, then untick “Autoreboot” in its settings.
Put the tar file you downloaded into the AP tab
Click start and wait for the installation to finish, Odin will show PASS.
Now hold down Power button and Volume down on Samsung M42 for about 10 seconds to force reboot the Samsung M42.
Immediately after the screen goes black release the keys and hold down Volume up and Power button at the same time until you enter TWRP. Keep in mind you may need to release the keys after about 20-30secs due to the “unlocked bootloader” warning.
If you properly followed all the steps you should now see the TWRP menu.
I highly recommend to flash multidisabler and services disabler right after you enter TWRP to disable forced encryption and stock recovery restoration.