UPDATE - Epic has since confirmed this to be true.
Epic revealed Unreal Engine 5 today, the next big step for the multiplatform engine used by countless developers. Along with a reveal trailer, Epic shared a very detailed blog on what Unreal Engine can do. Within that blog, you can find the following blurb.
Unreal Engine 5 will be available in preview in early 2021, and in full release late in 2021, supporting next-generation consoles, current-generation consoles, PC, Mac, iOS, and Android.
Unreal Engine 4 is supported on Switch and is certainly a current-gen platform, so it seems likely that Unreal Engine 5 will continue the Switch support. It may not have the full suite of features, but it'll definitely have improvements over what Unreal Engine 4 offers.