What has helped me is taking notes. I use Obsidian for note taking (I don't mean the app itself is the solution, just the one that works for me).
When I'm out and about I take notes whenever I think of something "oh, I should probably look into this book!" Or "make an app to do X and Y".
When I'm at home and I have nothing better to do I tidy up my notes. Sometimes doing this is an entertainment in itself, and sometimes this reminds me that I wanted to watch a certain movie and it's a great day for that.
I rarely get bored anymore because I capture the fleeting ideas I get through the day, and I'd need years to carry them all to fruition. On a given day reviewing my notes I might be interested only in 1 out of 10... But that's still one idea that keeps me busy and entertained, and then it's also something fulfilling because I've chosen it mindfully, unlike scrolling tiktok endlessly or watching whatever slop Netflix's algorithm force feeds me that day.