A quick guide to the movie's gaming background: In this movie we see a small group of programers tweaking an online game where people create their avatars (called their skin) to play against other people's avatars. Also, in this shootout fest are NPCs (non-playable characters) that seem real to us, but they're just programmed to be robotic background characters. Our main character is a NPC bank teller (called blue shirt guy; BSG) who through special glasses gains access to the non-real world he lives in, but in doing so his code now becomes self aware (i.e. AI or artificial intelligence) & begins to alter the game's code. The avatars gain points (money) by killing or picking up items. After so much money you "level up" - you're more powerful or gain access to other areas to explore.
An aside: Jodie Comer shows her versatility in a role quite distant from her "Killing Eve" disturbing character.
Also, ball park 500 people were in visual effects & digital artistry for the film's CGI.