There's no such thing as a "sole proprietorship LLC". Either it's a sole proprietorship, or it's a single member LLC. If the latter, then you had to register with the state and pay a fee to maintain that status in 2021, as well as 2022. Therefore, you had expenses.
If you were "open for business" in the tax year, weather you had income or not doesn't matter. I'm sure you still had expenses if you are "in fact" a legally registered LLC. Therefore you would file a tax return for each year starting with the tax year you were officially "open for business". If anything, so you could claim the expenses.
Take note that "in general" if your LLC does not show a profit in 3-5 years, that has the potential to get the attention of the IRS and they may question you on the legitimacy of your business.
Now if you were not officially open for business in 2021 or 2022, then you don't need to file a SCH C at all. I've seen situations where a business is established and it can take 3-5 years before they are officially capable of being open for business.
