The skills you're looking for fall into Android reverse engineering, firmware, rooting, bootloader, and recovery rather than just "installing ROMs."

Learning Roadmap

Level 1 — Android Internals (Start here)

Learn:

• Android boot process
• Partitions
• A/B partitions
• Dynamic partitions
• AVB (Android Verified Boot)
• dm-verity
• Recovery vs Bootloader vs Fastboot vs Download Mode
• Boot images
• Vendor partition
• Product partition
• System partition
• userdata

Tools

Ubuntu is perfect.

Install:

adb
fastboot
heimdall
android-sdk-platform-tools
git
python

You'll use these daily.

Level 2 — Samsung Specific

Samsung is different.

Samsung does not use Fastboot for flashing.

Instead it uses

• Download Mode
• Odin protocol

Learn:

• BL
• AP
• CP
• CSC
• HOME_CSC

Understand what each firmware file does.

Example firmware:

BL_A145F....
AP_A145F....
CP_A145F....
CSC_A145F....
HOME_CSC....

Level 3 — Firmware

Learn where firmware comes from.

Sites like:

• SamFW
• SamMobile
• Samsung Firmware Downloader tools

Learn:

• firmware regions (CSC)
• binary versions
• downgrade protection
• bootloader revisions

Level 4 — Flashing

Windows:

• Odin (Samsung's de facto flashing tool)

Linux:

• Heimdall

Learn:

Download Mode

↓

Flash AP

↓

Flash BL

↓

Flash CSC

↓

Recovery

Level 5 — Rooting

This is where things get interesting.

Learn:

Unlock bootloader

↓

Patch boot.img

↓

Magisk

↓

Flash patched image

↓

Root

Understand:

• vbmeta
• boot.img
• init_boot.img (Android 13+)
• recovery.img

Level 6 — Recovering Bricked Phones

You'll intentionally brick devices while learning.

Learn:

Boot loops

Soft brick

Recovery loop

Download Mode only

No download mode

FRP

OEM Lock

KG State

RMM State

Level 7 — Custom Recovery

Learn:

TWRP

OrangeFox

Why many modern Samsung phones don't have stable TWRP builds.

Level 8 — ROM Development

Eventually you'll understand

AOSP

LineageOS

Pixel Experience

Evolution X

Building Android

Kernel compilation

Device trees

Vendor blobs

Operating Systems

You don't need Windows except for Odin.

I recommend:

Ubuntu

Everything except Odin.

Windows VM (optional)

Only for Odin.

Most professionals keep both.

Software Stack

ADB

Fastboot

Heimdall

Odin

Magisk

7-Zip

Python

Git

VS Code

Android SDK Platform Tools

Samsung USB Drivers (Windows)

Reverse Engineering

This becomes incredibly useful.

Learn:

APKTool

JADX

Ghidra

Frida

Objection

Burp Suite

MobSF

ADB shell

logcat

dumpsys

pm

am

sqlite

Kernel / Boot

Understand

Boot ROM

↓

Bootloader

↓

AVB

↓

Kernel

↓

init

↓

System Server

↓

Launcher

Once you understand this flow, Android problems become much easier to diagnose.

Excellent Learning Resources

Android Internals

• The Android Open Source Project (AOSP) documentation
• Android Developers documentation

Samsung

• SamFW (firmware information and downloads)
• XDA Developers (arguably the best community for rooting, ROMs, and device-specific guides)

Reverse Engineering

• OWASP Mobile Application Security Testing Guide (MASTG)
• Android Security Internals by Nikolay Elenkov (book)

Linux

• Arch Wiki (many Android tooling topics are documented well even if you use Ubuntu)

Since you're interested in cybersecurity

This knowledge fits together well:

Linux
        ↓
ADB
        ↓
Android Internals
        ↓
Rooting
        ↓
Kernel
        ↓
Reverse Engineering
        ↓
Mobile Pentesting
        ↓
Malware Analysis

A word of caution about your A14

Because you mentioned the IMEI has already been modified, avoid using it on cellular networks for experimentation. Laws regarding IMEI modification vary significantly by country, and using a device with an altered IMEI on a public network can have legal consequences. As a lab device, it's much safer to keep it for offline testing, Wi-Fi, firmware flashing, rooting, and Android research.

📓 Obsidian Study Roadmap

Given what I know about your goals (backend, Linux, and cybersecurity), I'd structure it like this:

Phase 1
□ ADB Mastery
□ logcat
□ dumpsys
□ pm
□ am
□ content
□ settings
□ bugreport

Phase 2
□ Android Boot Process
□ Partitions
□ Recovery
□ Download Mode
□ AVB
□ dm-verity

Phase 3
□ Samsung Firmware
□ Odin
□ Heimdall
□ BL/AP/CP/CSC
□ CSC regions
□ Bootloader versions

Phase 4
□ Magisk
□ Boot image patching
□ init_boot
□ vbmeta
□ Rooting

Phase 5
□ APK Reverse Engineering
□ JADX
□ APKTool
□ Frida
□ Ghidra
□ MobSF

Phase 6
□ Build AOSP
□ Build LineageOS
□ Kernel compilation
□ Device trees
□ Vendor blobs

This progression takes you from basic device management to understanding and modifying the Android operating system itself, and it aligns well with a path into mobile security research.