There is unfortunately no one-size-fits-all answer for this question: it will be different for every game dev. We've set up a Wiki-style answer to help gather general advice.
One thing you should consider is survivorship bias. You're not seeing every game idea someone started working on. You're only seeing the ones:
...where the creator got far enough with the idea to share it
...where what they shared got popular enough to reach you through social media
...where what you saw was noteworthy enough for you to remember seeing it, etc.
So that means that the game ideas you remember seeing will skew very heavily toward the amazing/innovative/wow end of the spectrum, even if that's actually a very tiny fraction of these developers' total creative output.
Make enough small games and prototypes, and a few of them are bound to be good/clever. The best developers don't have better ideas than other folks, they just dive in and try things and and produce a lot of sketches/experiments/prototypes to explore different angles. Most of it is junk that gets thrown away. But with practice, they learn when to let something go or when to chase stuff that works. Sift enough silt, and you'll find a few grains of gold.
So, through that lens, and especially when starting out: prioritize quantity over quality. Paradoxically, racing through a tonne of garbage will help you learn more and take you farther than sitting in analysis paralysis trying to think of and polish that one perfect idea.
An old game development adage is "Your first 10 games will be terrible, so get them out of the way as fast as you can!"
Cross-pollinate: if you only look at existing games, you'll tend to make things that look like what you've seen before, or repeat the same mistakes. Spend some time doing something, anything else. Develop a non-gaming hobby, consume non-game media, cultivate non-game skills. Those outside influences will give you a unique perspective on life and your work, different from other players and developers, and that will inform your craft in big and small ways.
A great example of this is the much-lauded Nemesis System in Shadow of Mordor, that creates emergent narratives through your repeated encounters with orc chieftains and their movement through the ranks. In this GDC microtalk (starting around 50 minutes in), Michael de Plater discusses how this system was not created by just studying game narrative systems or the Lord of the Rings source material. Instead, the inspiration came from sports, and the rivalries that emerge between teams through the systemic interactions of tournaments and seasons.
Speaking of lenses, Jesse Schell's The Art of Game Design and its accompanying deck of lenses (available as a free mobile app) I find is a great source of inspiration.
The Art of Game Design: a Deck of Lenses (iOS)
The Art of Game Design: a Deck of Lenses (Android)
