[Samsung Galaxy Tab A series Guides, News, & Discus] thepalek1ng:
Hello!

So recently I was able to install LineageOS 18.1 (GSI) + GApps on my Samsung Galaxy Tab A 8 (SM-T290) tablet and wanted to share how I did it. I noticed a lack of decent step-by-step guides to modding this tablet so I figure I'd share what I learned through scouring multiple threads and through multiple headaches. Fun fact: I also got this working with LineageOS 19 (GSI), however it ran pretty poorly and Android 12 is ugly as hell so why bother anyway? ALSO interestingly enough, you'll see I wrote [SM-T290N] in the title as well. That is the model of the Kid's Edition of this phone, which happens to be the one I had. So I can confirm this process works for the Kid's Edition of this tablet as well as the original.

What You'll Need

Your tablet

A USB Cable to connect your tablet to your PC

A 4GB+ MicroSD card

A Windows PC

Some patience

Instructions

Preparing Your MicroSD Card

1. Place the LineageOS 18.1 .img file from this thread (On SourceForge, there is a section below the files about the naming conventions and how they relate to the hardware of your device and configuration of your ROM. I used the lineage-18.1-20220315-UNOFFICIAL-arm64_bvS-vndklite.img.xz image for my device. If your device is slightly different, you can use Treble Info to determine what ROM you should use. Just make sure to use the VNDKLITE rom if your device supports it.

2. Place the multidisabler .zip folder on there as well. This will preserve encryption provided by TWRP after rebooting.

3. Finally, place the MindTheGapps .zip folder on your SD card (make sure to get the correct version. In my case this was the 11.00-arm64 version).

4. Insert your MicroSD card into your device.

Unlocking the Bootloader

So the first thing you're gonna want to do is unlock your OEM bootloader on your Samsung device.

1. Go to Settings->About Phone->Software Information and look for a field called "Build Number". Tap this Five Times until you see a notification saying developer settings were enabled.

2. Go to Settings->Developer Settings and look for the setting labeled OEM Unlock and turn it on.

3. From here, you can reboot your device into Recovery Mode by holding the Vol+ and Vol- buttons when the device begins to boot again.

4. You should see a blue screen with some options. Press the Vol+ button to enter Download Mode. This is where you'll use Odin to flash the firmware you need as well as TWRP.

Flashing Firmware

So when I attempted this process I used Magendanz's Unofficial TWRP 3.6.0 as it is the only version of TWRP I found for this device. I also used Odin v3.14.1_3B Patched from this XDA thread. Magendanz's TWRP requires you to have the T290XXU3CUG4 Firmware (I used the XAR region) in order to flash TWRP to your device (you can check wether or not you already have this firmware on your phone by looking the About Phone section again). It takes a while to download though make sure you have some time.

1. Download Odin and run the program. Unzip your firmware folder and use the relevant files when selecting the BL, AP, CP, CSC fields in Odin. I didn't use the HOME_CSC just leave it blank.

2. Connect your device via USB and Flash this firmware to your device.

3. Once your device restarts, go through the setup process and then repeat the Unlocking the Bootloader instructions above in order to make sure it is unlocked again.

4. Reboot your device the same way as stated above.

Flashing TWRP

Before starting, be aware that after you flash TWRP to your device, your device will restart and attempt to open the stock system again. You're going to want to hold the Power and Vol+ buttons simultaneously. You will likely get a warning screen saying that the bootloader is unlocked and may ask you to do a factory reset, this (I believe) is fine. The key here is that once you press the Power Button to continue (as instructed on the warning screen) you'll want to immediately press and hold the Power and Vol+ keys for around 6 Seconds before letting go again (you should be seeing the Samsung Galaxy Tab A logo screen). After letting go, wait around 3-4 seconds, if nothing changes, restart the device by holding all three buttons (Power, Vol+,Vol-) and attempt the process again. It's a pain in the ass but you'll get it eventually. Just make sure not to let the device boot into the system again as that can cause problems in TWRP and you'll likely have to start the process over (from flashing the firmware).

1. Once your tablet is once again in Download Mode, open Odin again and flash the TWRP (tar.md5 file) to the AP (recovery) partition. Do not use any of the other partitions.

2. If this is successful, your phone will begin to reboot. Quickly press and hold the combination of buttons Power and Vol+ until you see the warning dialog pop up. Once you do, release all buttons and be ready to quickly press and release the Power button continue, and then immediately after press and hold the Power and Vol+ buttons again for 6 seconds. After around 6 seconds, release all buttons. Wait around 3-4 seconds and, if the screen does not change to the TWRP logo, restart the device by pressing and holding all buttons simultaneously and try this step again.

3. If you have entered into TWRP, congrats!

Installing Custom ROM + Software in TWRP

1. The first thing you'll want to do is select the Wipe->Format Data. Type 'yes' and hit enter (or swipe I forget which).

2. Next, select Install, and then select your MicroSD card as your storage device. You should see your zip files (if not switch from the install image option).

3. Install the multidisabler, do not reboot

4. Go back into Install and select Install Image (might not be the exact naming) option. Select your MicroSD card as the storage device again and install the LineageOS 18.1 rom. Do not reboot.

5. Go back into Install and select your MindTheGapps zip file and install it.

Final Steps

Once you reboot you should be able to successfully reach the setup screen for Lineage. Go through the steps of setting up your device as usual and be sure that Gapps are installed. Go ahead and re-enable developer settings and enable USB-Debugging and Root Debugging. The reason for this is that, when I first installed Gapps, Google Play Protect would keep throwing warnings at me about my device not being Google Play Certified. This means I couldn't actually use any of the google play services. If you run into the same issue, here are the steps you can take to fix it:

1. First, go into Settings->Apps and find your Google Play Services app. Clear the cache and delete the app data, then reboot your device. If you try and sign into the Google Play store and you are able to without getting any play protect warnings, then you're good you can disregard the following steps.

2. If you are still receiving these warnings, you'll want to head over to this site and follow the instructions (I'm not gonna tell you how to use ADB here). Once you submit your framework ID, reboot your device. Everything should be working fine now.

And that's it! If I am forgetting any steps please let me know, again I am writing this from memory of the process so it may be missing some minor details. I hope this helps!!!