For me it was pong on a computer with a 5 inch green screen built right into the computer and a drive bay just as big as the computer to read the disks like a floppy but bigger and thin

Pong frist second was frogger.. on the same green screen computer..

The first one I distinctly remember would have been Super Mario Bros. on my friend’s NES system.  I remember encountering an Atari but I think that was later.