[Samsung Galaxy A53 5G] mytja:
I'm also quite new to the scene, but Treble Info app shows "VNDK is not in lite mode", so I guess that means don't use `vndklite`. I unfortunately have made a mistake and tried installing Android 13 vndklite GSIs (Android 12 vndklite worked fine) on this device and yeah ... it took me a while to figure it out. So, go ahead and rather use VNDK (no -vndklite appendix).

Samsung Galaxy A53 5G is using the newer standard, not the legacy one (so A/B instead of A-only).

In GSI ROMs you'll find the following naming scheme for the first letter:

a = A-only (legacy, not supported in a lot of Android 13 GSIs)

b = A/B

And for the second letter:

g = proprietary Google apps preinstalled

o = proprietary Google Go (lightweight) apps preinstalled

v = vanilla (bare bones system with no additional apps preinstalled, only what's shipped in AOSP)

f = FLOSS apps (might include MicroG or other FLOSS alternatives, such as Aurora Store, F-Droid etc.)

The third letter represents the state of root on your system:

N = no superuser/root, always the right choice - if you don't want root, leave it like that and if you want root, go ahead and install Magisk/KernelSU - it won't collide with any other root options.

S = phhusson's SuperUser included (pre-rooted system). SuperUser is quite limited in what you can do and is considered legacy, but if you really don't want to mess around and just have root, it might be the way to go for you

Z = enhanced dynamic superuser. Rarely offered, haven't tested yet, but in any case I think it would be best to stick to N (no root).

So let's say you have the following requirements:

Google apps: YES (the standard apps, not lightweight ones)

SuperUser: NO, I'd rather install it later (or don't install it at all)

Per these requirements, you'd have to install an image with following parameters:

your_rom_name-arm64_bgN.img

Note that not every GSI uses these naming conventions. Pixel Experience Plus doesn't use these naming conventions, because they try to emulate the Pixel experience, which by default comes with proprietary Google apps and no superuser.

Do you have an Exynos device or Snapdragon one? I'm using an Exynos device and you might have to install IMS APK for Snapdragon devices (I'm not sure, I haven't used Snapdragon before, so I don't really know). For Exynos chip, everything should work out of the box.

You're currently using a ROM I presume. Do you have root (Magisk)? Magisk likes to interfere with IMS services from what I've seen on incorrect installation.

In case of that, you might want to reflash the stock ROM (OneUI that came with your phone) first and proceed with having no root/don't install any root solutions. Try to download latest firmware from Samsung and fill out all fields with respective .img or .tar files and flash it like it's new. Go through the entire setup process and when it's done you may flash the vbmeta and TWRP. After installing TWRP, make sure to run multidisabler and only then install the permissive kernel and system image of your GSI.

If your SIM works without root, we can easily diagnose the problem and build on top of that. In the end it might just be a faulty Magisk/root installation.

If you're confused with the process after setting up the Samsung's ROM, you should refer to the following thread.

https://xdaforums.com/t/recovery-unofficial-twrp-for-galaxy-a53-5g-exynos.4467443/