Thank you, Caro, but unfortunately I can't get to the AP .tar file downloaded from OTA. I have clean firmware. I was mo 8. But then something went wrong in my phone and I had to download the original firmware G975FXXU9EUA4 via sammobile. And so I have to do everything from the beginning. But I don't know how anymore. Your work is brilliant. Please advice. thank you very much
You need to get the firmware working before attempting to flash this mod. Here are some simple steps, the link I gave earlier goes into more detail.
Download EUA4 firmware, multidisabler and latest official TWRP image (not tar)
Download latest magisk app (v22)
Open firmware and transfer AP file to phone
Patch AP file and twrp with magisk
Transfer AP file and twrp back to computer
Open AP file and replace existing recovery with twrp (renamed to 'recovery')
Using odin flash firmware files (ap,bl,cp,csc), untick auto reboot
Once flash is successful reboot immediately to twrp using button combo (u will need to leave the phone connected to computer to be able to boot to twrp).
Twrp will automatically restart the phone, again reboot to twrp using button combo, without letting phone boot normally first.
Flash multidisabler
In twrp select reboot to recovery, allow phone to boot and set it up like normal.
If at this stage magisk wasn't successfully installed then you may need to use a customer kernel. This is easy to do.
Either use the twrp app to flash the unpatched twrp file or boot to twrp using key combo and flash unpatched twrp using twrp.
Then reboot to twrp (which will now be stock unpatched)
Flash customer kernel
Reboot to system not recovery (no need to use key combo if u have a custom kernel)
Once you have updated firmware working with magisk, all you need to do is flash the mod through twrp, restart phone, boot to twrp again and flash the theme.