Frame modifications are usually needed for low power e-bikes and absolutely required for high powered bikes.
There are several dropout options. Most of the commercial units are bolt on. Amped Bikes ebikes.ca
An excellent option is a 7075 aluminum milled bolt on drop outs for Norco frames.
One of the best generally (no going back) options are the water jet cut dropouts by doctorbass. These can be bolted up, but he (and we) like using DP420 epoxy to mount them.