The Safe Exam Browser (SEB) can be used in-class and remotely as long as it is installed on a student device.
For both in-class and remotely, SEB will lock everything within the device.
SEB, however, cannot prevent students from using resources outside the device, e.g. a 2nd device or a sheet with notes.
As it is significantly more difficult to prevent access to outside/2nd resources in a remote setup, we recommend using SEB primarily for in-class assessments only.