In custom scan open explorer and right click on say C drive. Should scan all C drive. Do same for This PC and I assume should do all drives. Will not do network though will if you select same and select scan. At least this what I think is the way it works.
I tried this and it is scanning C drive fine so I assume will do others after C finished. Cannot wait and watch have other things on sorry.
For several items select items holding down the ctl key
Alternative choose full scan it does all files that can be virus carriers. as well.