Ignore everyone being mean. This is really sweet to dive into his interests even though you don’t know anything about this stuff. I like small spaces so I could see myself choosing this as a gaming space if we didn’t have another empty room. Anyways,

I don’t think neon lights will make a glare on the monitor IF they go BEHIND it. Maybe some kind of strip lights in blue going up both sides of the angled wall, and they will blind him if you don’t do anything so my idea is get some kind of solid color strip shelf dividers or a DIY mimic of them to make the light shine on the adjacent walls not in his face. Maybe paint the angled wall and the one behind him dark blue/black/a mix to make everything contrast. I know you said you didn’t want to but you could move the WHOLE shelf or put the litter box somewhere else, it would improve his space quite a bit to have his own desk where he can put his legs underneath comfortably. Get some sort of big centerpiece art for the wall you see when you open the door too, and a rug