What studios actually look for in a game programmer's portfolio
I have sat on the interviewing side too. A few things repeat in the portfolios that stand out.
One finished thing beats ten half-finished ones
Show one completed project instead of ten prototypes. Finishing is a far harder skill than starting, and it is exactly what an employer is looking for.
"Completed" does not have to mean on a storefront. A demo with menus, settings, a save system and a proper ending screen counts too.
Explain why, not what
"I wrote an inventory system" tells me nothing. "I made the inventory ScriptableObject-based because designers needed to add items without writing code" shows a decision.
What is being assessed in a technical interview is almost always how you make decisions, not which library you used.
Give numbers
Instead of "I did optimisation", say "I cut frame time from 22 ms to 14 ms, and most of the win came from batching draw calls".
A measurable result shows both that the result is real and that you know how to measure. The second one matters more.
Make your code readable
If you link a GitHub repository, whoever opens it should understand what it does within thirty seconds. A README, a short architecture note and one screenshot are usually enough.
A recruiter who opens the repo and gets lost among hundreds of files will never see the quality of your code.