I built a conversion e-bike for my wife. She has a Specialized flat bar road bike. I bought the conversion kit from a UK company called Swytch. About $700 for the kit. Motor is in the front wheel, pickup on the crank to detect pedaling and battery/controls on the handlebars.
Unless you drop a lot of coin, most of the e-bikes are absolute crap. So now she has an e-bike that is a decent bike with assist that fits her. About 30 mile range, but she doesn’t want to ride further. And the bike rides nicely with the power off.