Try the list on True achievements for easy games.
https://www.trueachievements.com/games.aspxUnder 'More Filter Options, select 'other filter' and select Xbox Game Pass games (or Game Pass for PC if that's an option). Then click the Completion time header to sort by shortest to longest estimated completions.
Don't Starve is a 10 minute 1000G if you have access to a PC, and Subnautica is easily done with codes too. The first too Five Nights at Freddy's games are also exploitable on PC.
There's an hour long trial version of the game Pixark which can be maxed out in that time with codes. And a recent free game Rec Room which is an easy 700G. I'll have a think for some more stuff if anyone needs any more.