[Samsung Galaxy A20 Guides, News, & Discussion] very_cool:
I was able to do that with my SM-A205FN. My findings are below (PLEASE READ TO END IF YOU ARE NEWBIE)

Bootloader warning

Every A20 model has locked bootloader. In some posts regarding A20, it was said that you need to "enable OEM Unlocking in Developer Mode (if applicable)". This is misleading. You have to do OEM unlock EVERY time you re-install stock system - it locks bootloader, and to unlock it, you will have to make sure OEM Unlocking is visible in settings. If it is not visible, your bootloader may not be unlocked.

Fastboot and Samsung

You can only use Odin (Windows, strongly advised) or Heimdall (linux/MacOS).

Making OEM Unlock visible

1. disable system updates, security updates, auto-download updates in Settings. There are 3 different options for them

2. disable automatic date & date, and set date to exactly 1 month ago

3. connect your device to the internet and give Google services some time. Logging in to Google Account in Android Settings may help make OEM Unlocking visible if it does not appear in a minute with internet connection.

The right way to start bootloader download mode

It is described in "Unlocking bootloader" section of the OP. If you start bootloader this way, you see helpful messages in top-left corner, like RMM state and bootloader lock state (and warranty bit state). You will also see a red message there if Odin error "RQT_CLOSE !!" happens - "Only official released binaries are allowed to be flashed".

Unlocking bootloader will do a factory reset/wipe data with all settings for system time, updates, and developer mode. to fix Prenormal KG/RMM state, re-do these changes before connecting to the internet to fix Prenormal state. A reboot for safety after changing settings could be good idea.

KG/RMM State "Prenormal" fix

RMM State must be "Checking" to allow flashing. RMM State normally changes after 7 days of device "activation". I cannot find any info how it works. It just locks for 7 days, if you don't fake the datetime you set when enabled "OEM Unlocking".

After unlocking bootloader and then doing one or two reboots and connecting to the internet, my KG state changed to Checking. It is interesting, that if you flash stock system/AP back, your KG/RMM state will go to Prenormal again.

/sdcard is not writable means /data is encrypted.

Pay attention to the instructions from this post https://xdaforums.com/galaxy-a20/development/twrp-samsung-galaxy-a20-custom-recovery-t3955271 if you want to install custom ROMs, you will need to decrypt /data (/sdcard) partition. Decrypting /data fixes bootlooping of the stock system after TWRP install.

Soft bricking warning

To avoid bricking, ensure that you enable "OEM unlocking" in "Developer Mode" BEFORE rebooting stock system if TWRP is installed. Soft bricking will happen after reboot since stock firmware re-locks bootloader. This is just a precaution before you follow the TWRP process. If you missed and rebooted stock firmware with TWRP installed, you will lose recovery and system mode. However, Download mode will be available. Power off. After some time, hold volume buttons down and connect power cable to enter bootloader unlocking screen. This, however, was tricky to me to fix soft bricking.

My first custom ROM

I was able to flash custom ROM lineage-16.0-20190910-UNOFFICIAL-treble_arm64_bvN.img

Not _avN.img variant of it

The right way to do the flashing:

Follow instructions https://www.android-hilfe.de/forum/...iziell-pie-lineageos-16-0-andyvan.928318.html.

In short: wipe data first, then format it (all using TWRP buttons), then flash your System Img, reboot to recovery. This type, Flash ONLY Magisk ZIP, go to Wipe > advanced > select system > and use "Resize partition". After it will fail, second time should work. Wipe caches and reboot to system, it will restart several times before Lineage install will begin.

With that ROM, Wifi, SIM, Bluetooth, NFC connectivity works, fingerprint is working, front camera doesn't. MTP Doesn't work in practice, although it is supported. Seems like some fix is needed.

If this was helpful, hit THANKS button under this post.