I believe business ownership is the fastest, most reliable, and efficient path to FIRE there is. One, because no expensive college degree is required (plus the opportunity cost), and two, because business ownership opens the door wide for tax-sheltered investment vehicles.
I'll also mention that self-employment is most compatible with the "mission of FIRE" because you are, in essence, valuing your own time.
Many people think entrepreneurship means founding the next big tech startup or coming up with an amazing new product. This couldn't be more backwards. Why compete with Silicon Valley or China? You're competing against the brilliant people and cheap labor. These businesses are a dime a dozen and most fail. Not to mention having to invest your own money in such a business.
Starting a local service business and earning $100k+ within 1-3 years is attainable if you're willing to put in some sweat and make it happen. This can be done with almost no starting capital and because of that, very little risk of bankruptcy. You're competing with folks down the road still using 90s technology who are so busy making money that they don't return customer phone calls.
Here are some ideas for service businesses.
https://sweatystartup.com/businesses-i-love/Note: I love the overall message the Nick Huber preaches and have followed him since the early days, but lately there seems to be a lot of subscription courses being peddled from his site, so I no longer endorse him. You asked for a list of ideas, Sweaty Startup is a great place to start. I recommend this list and his general thought process on entrepreneurship, but not paid content. Hope this is clear.