Mainstream oscilloscopes typically have sampling frequency at least five times greater than the bandwidth of the analog front-end. For example 1 GHz bandwidth oscilloscope will have sample rate of 5 GSps.

https://www.tek.com/en/products/oscilloscopes https://www.keysight.com/us/en/catalog/key-34771/infiniivisi...

"Sampling" oscilloscopes are a much less common product -- they are useful for analyzing signals that are too fast to digitize in the ordinary way. They typically sample at a very slow repetition rate -- some hundreds of kilohertz, but each sampling aperture can be exceptionally short, allowing to record signals to 100 GHz frequency.

The BW of analog front end is where the amplitude drops in 3db. So if all you care is whether the signal is present and what is the frequency of it, you may get away with it.