Try searching on the devforum for ideas. You could think of games you like to play and what they do good or bad, and how they could be improved. I’m not saying you should copy them, but just get some ideas from them. Good luck!
This is a common question that gets asked and brought up around thousands of times already including often. Consider to search in the future to avoid duplicated questions that get repeated over again.
I’ll strive for simulators that haven’t been created - made in the platform to gather different ideas views things you do in real life try making unique simulators see what factors you could gather even use images online if necessary.
Always try making a simulator game that hasn’t been created there’s different ideas you could take, and approach try finding something your interesting in or enjoy the most if your into making simulators go for It. If you have a good idea planned out in your hand make it try to make the game feature a good game play and not something like clicking and holding down your space bar to gain in-game currency.
If your wanting to create some type of simulator game join different games and see what they have and see what you can do to improve the quality fo your game. (Making it different from others existing known games).