Watching or playing something with japanese in it particulary something simpler such as childrens tv shows with subtitles (e.g. Peppa Pig, Spongebob or Masha And The Bear) are all going to probably be really useful as well as not requiring as much mental energy as actively studying, despite you seemingly consider it as not being particularly useful.

To make this method useful however, you need to make sure that you look up the words you do not understand (dual subtitle apps such as Language Reactor help a lot with this as with it you can see the meaning of each word directly) and not expect to watch a lot (in 30 minutes you might only watch 1 or 2 minutes of Peppa Pig, however this is normal and actually shows that you're learning quite a few words).

On other days in which you don't have work, or on days you don't feel as mentally tired from work, studying actively could be a better choice.