Is there any way to play games from the middle?

On weekends, I really enjoy having evening sessions where I try out lots of games, both retro and current, jumping from one to another after 30-45 minutes of playing.

Usually, there's no problem because I've already started the ones I replay, so it's just a matter of launching them, regardless of how far I've progressed in the game, and playing for a while until I move on to the next one, doing random missions, advancing a chapter, or simply exploring the map. The problem arises with those I've never played before.

Usually, the beginning is the most tedious part of games (generally more so in modern games than in retro ones): restricted progress, mandatory tutorials and tips, blocked skills or maps...

Is there a website with savegames that aren't 100% complete, or some software that allows you to generate (or cheat) a savegame at 40% progress or something similar? Something like making your own demo, so to speak.

If any of this exists, or if you have any ideas, I'd love to hear them.

Thanks!