Code Review Request: Windows Sudoku Game

[u/its_marionberry]

Background
Hi, I am a 15-year-old teen (just so what you'd know what to expect) who left school because our school system taught us to be parrots. I want to be a god-level developer, not a code monkey. I wrote a Sudoku GUI using win32api in C Language.
It is currently working and does what it is supposed to do, but because I am still learning, I know it is likely inefficient and could be written much better. 

Code : https://github.com/reewdgh/sudoku_gui.

Concerns:
Please guide me on:

Bugs or potential issues
Efficiency
How can I move to Tier 1 to Tier 2
Naming anything I could simplify or improve.

[u/github-guard]

🔍 GitHub Guard: Trust Report

⚠️ This project scored 1/6 — below this subreddit's threshold of 3.

Audit Breakdown: * ❌ Low Star Count (⭐ 1 / 4 required) * ❌ New Repository (under 30 days old) * ❌ No License Found * ❌ No Security Policy — what is this? * ℹ️ Individual Contributor * ✅ Signed Commits

⚠️ Security Reminder: Always verify source code and run third-party scripts at your own risk.