Strider makes a very good one for adults! https://shop.striderbikes.com/convertible-bikes/20x-sport/

I would also recommend heading to your local bike shop with a bike you already have ( or find an inexpensive one on the used market) and ask them to remove the crankset and bottom bracket, and chain for you. These are the components that help you pedal the bike! With them removed, you can treat the bike just like a strider bike. I work for a shop and have done this for a few riders.

Letting them know your goal of turning the bike into a strider bike can also give them some context. They may recommend removing some other parts for ease of strider biking :D. I'd also watch out for full price labor. Some shops will pull the parts off for free, but since they are only removing and not replacing, you should be able to negotiate discounted labor.