Just an idea that I haven’t done myself or heard of anyone doing.
Randomly select 3 of your viable ideas. Put up 3 static sites with some marketing materials and/or “demos” without actually building anything.
Market them a little with word of mouth, social media, a few dollars of paid ads, cold emails, etc.
The one that gets the most pre-sales in a week or month or some timeframe is the one you build. Refund all of the other ones if they have pre-sales.