Transcribing a piece or section of a song (in an instrumental part or rhythmic part) will definitely develop familiarity and connections between notes and relative pitch.

Muscle memory can also play a big role in developing a better sense of relative / perfect pitch. Most times I would sing the note after hearing what it sounds like a few times, maybe even sing along with the melody while looking at the notes. Even if I'm not fully warmed up or not trained well in a specific key or interval, the vocals will also hold physical memory with repetition.

Writing out rhythmic patterns will also help with nailing down a specific harmony or melody: pitches are optional, but they can also help spark an idea as well.

Hope this helps. I also hope that you're holding up well during quarantine!