Technically yes, but the work for A and B may not be done at the same time so you may want to get a head start on getting A reviewed while B is still being worked on.

As a counter example. Why use multiple PRs when you can always just merge them into a single one. It's possible to make huge PRs with a bunch of different changes all included, but then the GitHub tools with managing stuff don't really work that well and you have to just do everything as comments instead of being about to actually accept a single accepted change for example.